Use autotools build system and add license

Signed-off-by: Nikias Bassen <nikias@gmx.li>

1 files changed, 1259 insertions, 0 deletions

diff --git a/src/usbmux.c b/src/usbmux.c
new file mode 100644
index 0000000..e86e3bc
--- /dev/null
+++ b/src/usbmux.c
@@ -0,0 +1,1259 @@
+/*
+ * Copyright (c) 2008 Jing Su. All Rights Reserved.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ * 
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ * 
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA 
+ */
+#include <stdint.h>
+#include <stdarg.h>
+#include <stdlib.h>
+#include <string.h>
+#include <usb.h>
+#include <stdio.h>
+#include <arpa/inet.h>
+#include <errno.h>
+#include <pthread.h>
+#include "usbmux.h"
+
+#define BULKIN 0x85
+#define BULKOUT 0x04
+#define HEADERLEN 28
+
+static const uint8_t TCP_FIN = 1;
+static const uint8_t TCP_SYN = 1 << 1;
+static const uint8_t TCP_RST = 1 << 2;
+static const uint8_t TCP_PSH = 1 << 3;
+static const uint8_t TCP_ACK = 1 << 4;
+static const uint8_t TCP_URG = 1 << 5;
+
+// I have trouble figuring out how to properly manage the windowing to
+// the device. It keeps sending back 512 and seems to drop off a cliff
+// when the device gets overwhelmed. In addition, the device likes to
+// panic and send out RESETS before the window hits zero. Also, waiting
+// for responses seems to not be a winning strategy.
+//
+// Since I'm not sure how in the hell to interpret the window sizes that
+// the device is sending back to us, I've figured out some magic number
+// constants which seem to work okay.
+static const uint32_t WINDOW_MAX = 5 * 1024;
+static const uint32_t WINDOW_INCREMENT = 512;
+
+typedef struct {
+	char *buffer;
+	int leftover;
+	int capacity;
+} receivebuf_t;
+
+struct usbmux_device_int {
+	struct usb_dev_handle *usbdev;
+	struct usb_device *__device;
+	receivebuf_t usbReceive;
+};
+
+typedef struct {
+	uint32_t type, length, major, minor, allnull;
+} usbmux_version_header;
+
+typedef struct {
+	uint32_t type, length;
+	uint16_t sport, dport;
+	uint32_t scnt, ocnt;
+	uint8_t offset, tcp_flags;
+	uint16_t window, nullnull, length16;
+} usbmux_tcp_header;
+
+struct usbmux_client_int {
+	usbmux_tcp_header *header;
+	usbmux_device_t device;
+
+	char *recv_buffer;
+	int r_len;
+	pthread_cond_t wait;
+
+	// this contains a conditional variable which usb-writers can wait
+	// on while waiting for window updates from the device.
+	pthread_cond_t wr_wait;
+	// I'm going to do something really cheesy here. We are going to 
+	// just record the most recent scnt that we are expecting to hear
+	// back on. We will actually halt progress by limiting the number
+	// of outstanding un-acked bulk sends that we have beamed out.
+	uint32_t wr_pending_scnt;
+	long wr_window;
+
+	pthread_mutex_t mutex;
+
+	// this variable is not protected by the mutex. This will always
+	// be E_SUCCESS, unless an error of some kind breaks this stream.
+	// this will then be set to the error that caused the broken stream.
+	// no further operations other than free_client will be allowed.
+	int error;
+
+	int cleanup;
+};
+
+
+static pthread_mutex_t usbmuxmutex = PTHREAD_MUTEX_INITIALIZER;
+static usbmux_client_t *connlist = NULL;
+static int clients = 0;
+
+
+/**
+ */
+int toto_debug = 0;
+
+void usbmux_set_debug(int e)
+{
+	toto_debug = e;
+}
+
+void log_debug_msg(const char *format, ...)
+{
+#ifndef STRIP_DEBUG_CODE
+	va_list args;
+	/* run the real fprintf */
+	va_start(args, format);
+
+	if (toto_debug)
+		vfprintf(stderr, format, args);
+
+	va_end(args);
+#endif
+}
+
+#ifdef DEBUG
+/**
+ * for debugging purposes.
+ */
+static void print_buffer(const char *data, const int length)
+{
+	if (toto_debug <= 0) {
+		return;
+	}
+	int i;
+	int j;
+	unsigned char c;
+
+	for (i = 0; i < length; i += 16) {
+		printf("%04x: ", i);
+		for (j = 0; j < 16; j++) {
+			if (i + j >= length) {
+				printf("   ");
+				continue;
+			}
+			printf("%02hhx ", *(data + i + j));
+		}
+		printf("  | ");
+		for (j = 0; j < 16; j++) {
+			if (i + j >= length)
+				break;
+			c = *(data + i + j);
+			if ((c < 32) || (c > 127)) {
+				printf(".");
+				continue;
+			}
+			printf("%c", c);
+		}
+		printf("\n");
+	}
+	printf("\n");
+}
+#endif
+
+void hton_header(usbmux_tcp_header * hdr)
+{
+	if (hdr) {
+		hdr->length = htonl(hdr->length);
+		hdr->scnt = htonl(hdr->scnt);
+		hdr->ocnt = htonl(hdr->ocnt);
+		hdr->length16 = htons(hdr->length16);
+	}
+}
+
+void ntoh_header(usbmux_tcp_header * hdr)
+{
+	if (hdr) {
+		hdr->length = ntohl(hdr->length);
+		hdr->scnt = ntohl(hdr->scnt);
+		hdr->ocnt = ntohl(hdr->ocnt);
+		hdr->length16 = ntohs(hdr->length16);
+	}
+}
+
+/** Creates a USBMux header containing version information
+ * 
+ * @return A USBMux header
+ */
+usbmux_version_header *version_header()
+{
+	usbmux_version_header *version =
+		(usbmux_version_header *) malloc(sizeof(usbmux_version_header));
+	version->type = 0;
+	version->length = htonl(20);
+	version->major = htonl(1);
+	version->minor = 0;
+	version->allnull = 0;
+	return version;
+}
+
+/**
+ * This function sets the configuration of the given device to 3
+ * and claims the interface 1. If usb_set_configuration fails, it detaches
+ * the kernel driver that blocks the device, and retries configuration.
+ *
+ * @param device which device to configure
+ */
+static int usbmux_config_usb_device(usbmux_device_t device)
+{
+	int ret;
+	int bytes;
+	char buf[512];
+
+#if 0
+	log_debug_msg("checking configuration...\n");
+	if (device->__device->config->bConfigurationValue != 3) {
+		log_debug_msg
+			("WARNING: usb device configuration is not 3 as expected!\n");
+	}
+
+	log_debug_msg("setting configuration...\n");
+	ret = usb_set_configuration(device->device, 3);
+	if (ret != 0) {
+		log_debug_msg("Hm, usb_set_configuration returned %d: %s\n", ret,
+					  strerror(-ret));
+#if LIBUSB_HAS_GET_DRIVER_NP
+		log_debug_msg("trying to fix:\n");
+		log_debug_msg("-> detaching kernel driver... ");
+		ret =
+			usb_detach_kernel_driver_np(device->device,
+										device->__device->config->
+										interface->altsetting->
+										bInterfaceNumber);
+		if (ret != 0) {
+			log_debug_msg("usb_detach_kernel_driver_np returned %d: %s\n",
+						  ret, strerror(-ret));
+		} else {
+			log_debug_msg("done.\n");
+			log_debug_msg("setting configuration again... ");
+			ret = usb_set_configuration(device->device, 3);
+			if (ret != 0) {
+				log_debug_msg
+					("Error: usb_set_configuration returned %d: %s\n", ret,
+					 strerror(-ret));
+				log_debug_msg("--> trying to continue anyway...\n");
+			} else {
+				log_debug_msg("done.\n");
+			}
+		}
+#else
+		log_debug_msg("--> trying to continue anyway...\n");
+#endif
+	} else {
+		log_debug_msg("done.\n");
+	}
+#endif
+
+	log_debug_msg("claiming interface... ");
+	ret = usb_claim_interface(device->usbdev, 1);
+	if (ret != 0) {
+		log_debug_msg("Error: usb_claim_interface returned %d: %s\n", ret,
+					  strerror(-ret));
+		return -ENODEV;
+	} else {
+		log_debug_msg("done.\n");
+	}
+
+	do {
+		bytes = usb_bulk_read(device->usbdev, BULKIN, buf, 512, 800);
+	} while (bytes > 0);
+
+	return 0;
+}
+
+/**
+ * Given a USB bus and device number, returns a device handle to the device on
+ * that bus. To aid compatibility with future devices, this function does not
+ * check the vendor and device IDs! To do that, you should use
+ * usbmux_get_device() or a system-specific API (e.g. HAL).
+ *
+ * @param bus_n The USB bus number.
+ * @param dev_n The USB device number.
+ * @param device A pointer to a usbmux_device_t, which must be set to NULL upon
+ *      calling usbmux_get_specific_device, which will be filled with a device
+ *      descriptor on return. 
+ * @return 0 if ok, otherwise a negative errno value.
+ */
+int usbmux_get_specific_device(int bus_n, int dev_n,
+							   usbmux_device_t * device)
+{
+	struct usb_bus *bus;
+	struct usb_device *dev;
+	usbmux_version_header *version;
+	int bytes = 0;
+
+	//check we can actually write in device
+	if (!device || (device && *device))
+		return -EINVAL;
+
+	usbmux_device_t newdevice =
+		(usbmux_device_t) malloc(sizeof(struct usbmux_device_int));
+
+	// Initialize the struct
+	newdevice->usbdev = NULL;
+	newdevice->__device = NULL;
+
+	// don't forget these:
+	newdevice->usbReceive.buffer = NULL;
+	newdevice->usbReceive.leftover = 0;
+	newdevice->usbReceive.capacity = 0;
+
+	// Initialize libusb
+	usb_init();
+	usb_find_busses();
+	usb_find_devices();
+
+	// Set the device configuration
+	for (bus = usb_get_busses(); bus; bus = bus->next)
+		//if (bus->location == bus_n)
+		for (dev = bus->devices; dev != NULL; dev = dev->next)
+			if (dev->devnum == dev_n) {
+				newdevice->__device = dev;
+				newdevice->usbdev = usb_open(newdevice->__device);
+				if (usbmux_config_usb_device(newdevice) == 0) {
+					goto found;
+				}
+			}
+
+	usbmux_free_device(newdevice);
+
+	log_debug_msg("usbmux_get_specific_device: device not found\n");
+	return -ENODEV;
+
+  found:
+	// Send the version command to the device
+	version = version_header();
+	bytes =
+		usb_bulk_write(newdevice->usbdev, BULKOUT, (char *) version,
+					   sizeof(*version), 800);
+	if (bytes < 20) {
+		log_debug_msg("%s: libusb did NOT send enough!\n", __func__);
+		if (bytes < 0) {
+			log_debug_msg("%s: libusb gave me the error %d: %s (%s)\n",
+						  __func__, bytes, usb_strerror(),
+						  strerror(-bytes));
+		}
+	}
+	// Read the device's response
+	bytes =
+		usb_bulk_read(newdevice->usbdev, BULKIN, (char *) version,
+					  sizeof(*version), 800);
+
+	// Check for bad response
+	if (bytes < 20) {
+		free(version);
+		usbmux_free_device(newdevice);
+		log_debug_msg("%s: Invalid version message -- header too short.\n",
+					  __func__);
+		if (bytes < 0) {
+			log_debug_msg("%s: libusb error message %d: %s (%s)\n",
+						  __func__, bytes, usb_strerror(),
+						  strerror(-bytes));
+			return bytes;
+		}
+		return -EBADMSG;
+	}
+	// Check for correct version
+	if (ntohl(version->major) == 1 && ntohl(version->minor) == 0) {
+		// We're all ready to roll.
+		log_debug_msg("%s: success\n", __func__);
+		free(version);
+		*device = newdevice;
+		return 0;
+	} else {
+		// Bad header
+		usbmux_free_device(newdevice);
+		free(version);
+		log_debug_msg("%s: Received a bad header/invalid version number.",
+					  __func__);
+		return -EBADMSG;
+	}
+
+	// If it got to this point it's gotta be bad
+	log_debug_msg("%s: Unknown error.\n", __func__);
+	usbmux_free_device(newdevice);
+	free(version);
+	return -EBADMSG;			// if it got to this point it's gotta be bad
+}
+
+/** Cleans up an usbmux_device_t structure, then frees the structure itself.
+ * This is a library-level function; deals directly with the device to tear
+ *  down relations, but otherwise is mostly internal.
+ * 
+ * @param device A pointer to an usbmux_device_t structure.
+ */
+int usbmux_free_device(usbmux_device_t device)
+{
+	char buf[512];
+	int bytes;
+
+	if (!device)
+		return -EINVAL;
+	int ret = 0;
+
+	if (device->usbdev) {
+		do {
+			bytes = usb_bulk_read(device->usbdev, BULKIN, buf, 512, 800);
+		} while (bytes > 0);
+	}
+
+	if (bytes < 0) {
+		ret = bytes;
+	}
+
+	if (device->usbReceive.buffer) {
+		free(device->usbReceive.buffer);
+	}
+	if (device->usbdev) {
+		usb_release_interface(device->usbdev, 1);
+		usb_close(device->usbdev);
+		ret = 0;
+	}
+	free(device);
+
+	return ret;
+}
+
+
+
+/** Sends data to the device
+ * This is a low-level (i.e. directly to device) function.
+ * 
+ * @param device The device to send data to
+ * @param data The data to send
+ * @param datalen The length of the data
+ * @return The number of bytes sent, or -ERRNO on error
+ */
+int send_to_device(usbmux_device_t device, char *data, int datalen)
+{
+	if (!device)
+		return -EINVAL;
+
+	int timeout = 1000;
+	int retrycount = 0;
+	int bytes = 0;
+
+#ifdef DEBUG
+#ifdef DEBUG_MORE
+	printf("===============================\n%s: trying to send\n",
+		   __func__);
+	print_buffer(data, datalen);
+	printf("===============================\n");
+#endif
+#endif
+	do {
+		if (retrycount > 3) {
+			log_debug_msg
+				("EPIC FAIL! aborting on retry count overload.\n");
+			return -ECOMM;
+		}
+
+		bytes =
+			usb_bulk_write(device->usbdev, BULKOUT, data, datalen,
+						   timeout);
+		if (bytes == -ETIMEDOUT) {
+			// timed out waiting for write.
+			log_debug_msg("usb_bulk_write timeout error.\n");
+			return bytes;
+		} else if (bytes < 0) {
+			log_debug_msg
+				("usb_bulk_write failed with error. err:%d (%s)(%s)\n",
+				 bytes, usb_strerror(), strerror(-bytes));
+			return bytes;
+		} else if (bytes == 0) {
+			log_debug_msg("usb_bulk_write sent nothing. retrying.\n");
+			timeout = timeout * 4;
+			retrycount++;
+			continue;
+		} else if (bytes < datalen) {
+			log_debug_msg
+				("usb_bulk_write failed to send full dataload. %d of %d\n",
+				 bytes, datalen);
+			timeout = timeout * 4;
+			retrycount++;
+			data += bytes;
+			datalen -= bytes;
+			continue;
+		}
+	} while (0);				// fall out
+
+#ifdef DEBUG
+	if (bytes > 0) {
+		if (toto_debug > 0) {
+			printf(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>\n");
+			printf("%s: sent to device\n", __func__);
+			print_buffer(data, bytes);
+			printf(">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>\n");
+		}
+	}
+#endif
+	return bytes;
+}
+
+/** Receives data from the device
+ * This function is a low-level (i.e. direct from device) function.
+ * 
+ * @param device The device to receive data from
+ * @param data Where to put data read
+ * @param datalen How much data to read in
+ * @param timeout How many milliseconds to wait for data
+ * 
+ * @return How many bytes were read in, or -1 on error.
+ */
+int recv_from_device_timeout(usbmux_device_t device, char *data,
+							 int datalen, int timeoutmillis)
+{
+	if (!device)
+		return -EINVAL;
+	//log_debug_msg("%s: attempting to receive %i bytes\n", __func__, datalen);
+
+	int bytes =
+		usb_bulk_read(device->usbdev, BULKIN, data, datalen,
+					  timeoutmillis);
+	// There are some things which are errors, others which are no problem.
+	// It's not documented in libUSB, but it seems that the error values
+	// returned are just negated ERRNO values.
+	if (bytes < 0) {
+		if (bytes == -ETIMEDOUT) {
+			// ignore this. it just means timeout reached before we
+			//  picked up any data. no problem.
+			return 0;
+		} else {
+			fprintf(stderr, "%s: libusb gave me the error %d: %s (%s)\n",
+					__func__, bytes, usb_strerror(), strerror(-bytes));
+			log_debug_msg("%s: libusb gave me the error %d: %s (%s)\n",
+						  __func__, bytes, usb_strerror(),
+						  strerror(-bytes));
+		}
+		return bytes;
+	}
+#ifdef DEBUG
+	if (bytes > 0) {
+		if (toto_debug > 0) {
+			printf("<<<<<<<<<<<<<<<<<<<<<<<<<<<\n");
+			printf("%s: received from device:\n", __func__);
+			print_buffer(data, bytes);
+			printf("<<<<<<<<<<<<<<<<<<<<<<<<<<<\n");
+		}
+	}
+#endif
+
+	return bytes;
+}
+
+/** Creates a USBMux packet for the given set of ports.
+ * 
+ * @param s_port The source port for the connection.
+ * @param d_port The destination port for the connection.
+ *
+ * @return A USBMux packet
+ */
+usbmux_tcp_header *new_mux_packet(uint16_t s_port, uint16_t d_port)
+{
+	usbmux_tcp_header *conn =
+		(usbmux_tcp_header *) malloc(sizeof(usbmux_tcp_header));
+	conn->type = htonl(6);
+	conn->length = HEADERLEN;
+	conn->sport = htons(s_port);
+	conn->dport = htons(d_port);
+	conn->scnt = 0;
+	conn->ocnt = 0;
+	conn->offset = 0x50;
+	conn->window = htons(0x0200);
+	conn->nullnull = 0x0000;
+	conn->length16 = HEADERLEN;
+	return conn;
+}
+
+
+/** Removes a connection from the list of connections made.
+ * The list of connections is necessary for buffering.
+ * 
+ * @param connection The connection to delete from the tracking list.
+ */
+static void delete_connection(usbmux_client_t connection)
+{
+	usbmux_client_t *newlist = NULL;
+
+	pthread_mutex_lock(&usbmuxmutex);
+
+	// update the global list of connections
+	if (clients > 1) {
+		newlist =
+			(usbmux_client_t *) malloc(sizeof(usbmux_client_t) *
+									   (clients - 1));
+		int i = 0, j = 0;
+		for (i = 0; i < clients; i++) {
+			if (connlist[i] == connection)
+				continue;
+			else {
+				newlist[j] = connlist[i];
+				j++;
+			}
+		}
+	}
+	if (connlist) {
+		free(connlist);
+	}
+	connlist = newlist;
+	clients--;
+
+	// free up this connection
+	pthread_mutex_lock(&connection->mutex);
+	if (connection->recv_buffer) {
+		free(connection->recv_buffer);
+		connection->recv_buffer = NULL;
+	}
+	if (connection->header) {
+		free(connection->header);
+		connection->header = NULL;
+	}
+	connection->r_len = 0;
+	pthread_mutex_unlock(&connection->mutex);
+	pthread_mutex_destroy(&connection->mutex);
+	free(connection);
+
+	pthread_mutex_unlock(&usbmuxmutex);
+}
+
+/** Adds a connection to the list of connections made.
+ * The connection list is necessary for buffering.
+ *
+ * @param connection The connection to add to the global list of connections.
+ */
+
+static void add_connection(usbmux_client_t connection)
+{
+	pthread_mutex_lock(&usbmuxmutex);
+	usbmux_client_t *newlist =
+		(usbmux_client_t *) realloc(connlist,
+									sizeof(usbmux_client_t) * (clients +
+															   1));
+	newlist[clients] = connection;
+	connlist = newlist;
+	clients++;
+	pthread_mutex_unlock(&usbmuxmutex);
+}
+
+/**
+ * Get a source port number that is not used by one of our connections
+ * This is needed for us to make sure we are not sending on another
+ * connection.
+ */
+static uint16_t get_free_port()
+{
+	int i;
+	uint16_t newport = 30000;
+	int cnt = 0;
+
+	pthread_mutex_lock(&usbmuxmutex);
+	while (1) {
+		cnt = 0;
+		for (i = 0; i < clients; i++) {
+			if (ntohs(connlist[i]->header->sport) == newport) {
+				cnt++;
+			}
+		}
+		if (cnt == 0) {
+			// newport is not used in our list of connections!
+			break;
+		} else {
+			newport++;
+			if (newport < 30000) {
+				// if all ports from 30000 to 65535 are in use,
+				// the value wraps (16-bit overflow)
+				// return 0, no port is available.
+				// This should not happen, but just in case ;)
+				newport = 0;
+				break;
+			}
+		}
+	}
+	pthread_mutex_unlock(&usbmuxmutex);
+
+	return newport;
+}
+
+/** Initializes a connection to 'device' with source port s_port and destination port d_port
+ *
+ * @param device The device to initialize a connection on.
+ * @param src_port The source port
+ * @param dst_port The destination port -- 0xf27e for lockdownd. 
+ * @param client A mux TCP header for the connection which is used for tracking and data transfer.
+ * @return 0 on success, a negative errno value otherwise.
+ */
+int usbmux_new_client(usbmux_device_t device, uint16_t src_port,
+					  uint16_t dst_port, usbmux_client_t * client)
+{
+	if (!device || !dst_port)
+		return -EINVAL;
+
+	src_port = get_free_port();
+
+	if (!src_port) {
+		// this is a special case, if we get 0, this is not good, so
+		return -EISCONN;		// TODO: error code suitable?
+	}
+	// Initialize connection stuff
+	usbmux_client_t new_connection =
+		(usbmux_client_t) malloc(sizeof(struct usbmux_client_int));
+	new_connection->header = new_mux_packet(src_port, dst_port);
+
+	// send TCP syn
+	if (new_connection && new_connection->header) {
+		int err = 0;
+		new_connection->header->tcp_flags = TCP_SYN;
+		new_connection->header->length = new_connection->header->length;
+		new_connection->header->length16 =
+			new_connection->header->length16;
+		new_connection->header->scnt = 0;
+		new_connection->header->ocnt = 0;
+		new_connection->device = device;
+		new_connection->recv_buffer = NULL;
+		new_connection->r_len = 0;
+		pthread_cond_init(&new_connection->wait, NULL);
+		pthread_mutex_init(&new_connection->mutex, NULL);
+		pthread_cond_init(&new_connection->wr_wait, NULL);
+		new_connection->wr_pending_scnt = 0;
+		new_connection->wr_window = 0;
+		add_connection(new_connection);
+		new_connection->error = 0;
+		new_connection->cleanup = 0;
+		hton_header(new_connection->header);
+		log_debug_msg("%s: send_to_device (%d --> %d)\n", __func__,
+					  ntohs(new_connection->header->sport),
+					  ntohs(new_connection->header->dport));
+		err =
+			send_to_device(device, (char *) new_connection->header,
+						   sizeof(usbmux_tcp_header));
+		if (err >= 0) {
+			*client = new_connection;
+			return 0;
+		} else {
+			delete_connection(new_connection);
+			return err;
+		}
+	}
+	// if we get to this point it's probably bad
+	return -ENOMEM;
+}
+
+/** Cleans up the given USBMux connection.
+ * @note Once a connection is closed it may not be used again.
+ * 
+ * @param connection The connection to close.
+ *
+ * @return 0 on success or a negative errno value on error.
+ */
+int usbmux_free_client(usbmux_client_t client)
+{
+	if (!client || !client->device)
+		return -EINVAL;
+
+	int err = 0;
+	int result = 0;
+	pthread_mutex_lock(&client->mutex);
+	client->header->tcp_flags = TCP_FIN;
+	client->header->length = 0x1C;
+	client->header->window = 0;
+	client->header->length16 = 0x1C;
+	hton_header(client->header);
+
+	err =
+		send_to_device(client->device, (char *) client->header,
+					   sizeof(usbmux_tcp_header));
+	if (err < 0) {
+		log_debug_msg("%s: error sending TCP_FIN\n", __func__);
+		result = err;
+	}
+
+	client->cleanup = 1;
+
+	// make sure we don't have any last-minute laggards waiting on this.
+	// I put it after the mutex unlock because we have cases where the
+	// conditional wait is dependent on re-grabbing that mutex.
+	pthread_cond_broadcast(&client->wait);
+	pthread_cond_destroy(&client->wait);
+	pthread_cond_broadcast(&client->wr_wait);
+	pthread_cond_destroy(&client->wr_wait);
+
+	pthread_mutex_unlock(&client->mutex);
+
+	return result;
+}
+
+/** Sends the given data over the selected connection.
+ *
+ * @param client The client we're sending data on.
+ * @param data A pointer to the data to send.
+ * @param datalen How much data we're sending.
+ * @param sent_bytes The number of bytes sent, minus the header (28)
+ *
+ * @return 0 on success or a negative errno value on error.
+ */
+int usbmux_send(usbmux_client_t client, const char *data, uint32_t datalen,
+				uint32_t * sent_bytes)
+{
+	if (!client->device || !client || !sent_bytes)
+		return -EINVAL;
+
+	if (client->error < 0) {
+		return client->error;
+	}
+
+	*sent_bytes = 0;
+	pthread_mutex_lock(&client->mutex);
+
+	int sendresult = 0;
+	uint32_t blocksize = 0;
+	if (client->wr_window <= 0) {
+		struct timespec ts;
+		clock_gettime(CLOCK_REALTIME, &ts);
+		//ts.tv_sec += 1;
+		ts.tv_nsec += 750 * 1000;
+		if (pthread_cond_timedwait(&client->wait, &client->mutex, &ts) ==
+			ETIMEDOUT) {
+			// timed out. optimistically grow the window and try to make progress
+			client->wr_window += WINDOW_INCREMENT;
+		}
+	}
+
+	blocksize = sizeof(usbmux_tcp_header) + datalen;
+
+	// client->scnt and client->ocnt should already be in host notation...
+	// we don't need to change them juuuust yet. 
+	char *buffer = (char *) malloc(blocksize + 2);	// allow 2 bytes of safety padding
+	// Set the length
+	client->header->length = blocksize;
+	client->header->length16 = blocksize;
+
+	// Put header into big-endian notation
+	hton_header(client->header);
+	// Concatenation of stuff in the buffer.
+	memcpy(buffer, client->header, sizeof(usbmux_tcp_header));
+	memcpy(buffer + sizeof(usbmux_tcp_header), data, datalen);
+
+	log_debug_msg("%s: send_to_device(%d --> %d)\n", __func__,
+				  ntohs(client->header->sport),
+				  ntohs(client->header->dport));
+	sendresult = send_to_device(client->device, buffer, blocksize);
+	// Now that we've sent it off, we can clean up after our sloppy selves.
+	if (buffer)
+		free(buffer);
+
+	// revert header fields that have been swapped before trying to send
+	ntoh_header(client->header);
+
+	// update counts ONLY if the send succeeded.
+	if ((uint32_t) sendresult == blocksize) {
+		// Re-calculate scnt
+		client->header->scnt += datalen;
+		client->wr_window -= blocksize;
+	}
+
+	pthread_mutex_unlock(&client->mutex);
+
+	if (sendresult == -ETIMEDOUT || sendresult == 0) {
+		// no problem for now...
+		*sent_bytes = 0;
+		return -ETIMEDOUT;
+	} else if (sendresult < 0) {
+		return sendresult;
+	} else if ((uint32_t) sendresult == blocksize) {
+		// actual number of data bytes sent.
+		*sent_bytes = sendresult - HEADERLEN;
+		return 0;
+	} else {
+		fprintf(stderr,
+				"usbsend managed to dump a packet that is not full size. %d of %d\n",
+				sendresult, blocksize);
+		return -EBADMSG;
+	}
+}
+
+/** append the packet's DATA to the receive buffer for the client.
+ *
+ *  this has a few other corner-case functions:
+ *  1. this will properly handle the handshake syn+ack.
+ *  2. for all receives, this will appropriately update the ocnt.
+ * 
+ * @return number of bytes consumed (header + data)
+ */
+uint32_t append_receive_buffer(usbmux_client_t client, char *packet)
+{
+	if (client == NULL || packet == NULL)
+		return 0;
+
+	usbmux_tcp_header *header = (usbmux_tcp_header *) packet;
+	char *data = &packet[HEADERLEN];
+	uint32_t packetlen = ntohl(header->length);
+	uint32_t datalen = packetlen - HEADERLEN;
+
+	int dobroadcast = 0;
+
+	pthread_mutex_lock(&client->mutex);
+
+	// we need to handle a few corner case tasks and book-keeping which
+	// falls on our responsibility because we are the ones reading in
+	// feedback.
+	if (client->header->scnt == 0 && client->header->ocnt == 0) {
+		log_debug_msg("client is still waiting for handshake.\n");
+		if (header->tcp_flags == (TCP_SYN | TCP_ACK)) {
+			log_debug_msg("yes, got syn+ack ; replying with ack.\n");
+			client->header->tcp_flags = TCP_ACK;
+			client->header->length = sizeof(usbmux_tcp_header);
+			client->header->length16 = sizeof(usbmux_tcp_header);
+			client->header->scnt += 1;
+			client->header->ocnt = header->ocnt;
+			hton_header(client->header);
+			// push it to USB
+			// TODO: need to check for error in the send here.... :(
+			log_debug_msg("%s: send_to_device (%d --> %d)\n", __func__,
+						  ntohs(client->header->sport),
+						  ntohs(client->header->dport));
+			if (send_to_device
+				(client->device, (char *) client->header,
+				 sizeof(usbmux_tcp_header)) <= 0) {
+				log_debug_msg("%s: error when pushing to usb...\n",
+							  __func__);
+			}
+			// need to revert some of the fields back to host notation.
+			ntoh_header(client->header);
+		} else {
+			client->error = -ECONNABORTED;
+			// woah... this connection failed us.
+			// TODO: somehow signal that this stream is a no-go.
+			log_debug_msg("WOAH! client failed to get proper syn+ack.\n");
+		}
+	}
+	// update TCP counters and windows.
+	//
+	// save the window that we're getting from the USB device.
+	// apparently the window is bigger than just the 512 that's typically
+	// advertised. iTunes apparently shifts this value by 8 to get a much
+	// larger number.
+	if (header->tcp_flags & TCP_RST) {
+		client->error = -ECONNRESET;
+
+		if (datalen > 0) {
+			char e_msg[128];
+			e_msg[0] = 0;
+			if (datalen > 1) {
+				memcpy(e_msg, data + 1, datalen - 1);
+				e_msg[datalen - 1] = 0;
+			}
+			// fetch the message
+			switch (data[0]) {
+			case 0:
+				// this is not an error, it's just a status message.
+				log_debug_msg("received status message: %s\n", e_msg);
+				datalen = 0;
+				break;
+			case 1:
+				log_debug_msg("received error message: %s\n", e_msg);
+				datalen = 0;
+				break;
+			default:
+				log_debug_msg
+					("received unknown message (type 0x%02x): %s\n",
+					 data[0], e_msg);
+				//datalen = 0; // <-- we let this commented out for testing
+				break;
+			}
+		} else {
+			log_debug_msg
+				("peer sent connection reset. setting error: %d\n",
+				 client->error);
+		}
+	}
+	// the packet's ocnt tells us how much of our data the device has received.
+	if (header->tcp_flags & TCP_ACK) {
+		// this is a hacky magic number condition. it seems that once
+		// the window reported by the device starts to drop below this
+		// number, we quickly fall into connection reset problems.
+		// Once we see the reported window size start falling off,
+		// ut off and wait for solid acks to come back.
+		if (ntohs(header->window) < 256)
+			client->wr_window = 0;
+
+		// check what just got acked.
+		if (ntohl(header->ocnt) < client->header->scnt) {
+			// we got some kind of ack, but it hasn't caught up
+			// with the pending that have been sent.
+			pthread_cond_broadcast(&client->wr_wait);
+		} else if (ntohl(header->ocnt) >
+				   /*client->wr_pending_scnt */ client->header->scnt) {
+			fprintf(stderr,
+					"WTF?! acks overtook pending outstanding.  %u,%u\n",
+					ntohl(header->ocnt), client->wr_pending_scnt);
+		} else {
+			// reset the window
+			client->wr_window = WINDOW_MAX;
+			pthread_cond_broadcast(&client->wr_wait);
+		}
+	}
+	// the packet's scnt will be our new ocnt.
+	client->header->ocnt = ntohl(header->scnt);
+
+	// ensure there is enough space, either by first malloc or realloc
+	if (datalen > 0) {
+		log_debug_msg("%s: putting %d bytes into client's recv_buffer\n",
+					  __func__, datalen);
+		if (client->r_len == 0)
+			dobroadcast = 1;
+
+		if (client->recv_buffer == NULL) {
+			client->recv_buffer = malloc(datalen);
+			client->r_len = 0;
+		} else {
+			client->recv_buffer =
+				realloc(client->recv_buffer, client->r_len + datalen);
+		}
+
+		memcpy(&client->recv_buffer[client->r_len], data, datalen);
+		client->r_len += datalen;
+	}
+
+	pthread_mutex_unlock(&client->mutex);
+
+	// I put this outside the mutex unlock just so that when the threads
+	// wake, we don't have to do another round of unlock+try to grab.
+	if (dobroadcast)
+		pthread_cond_broadcast(&client->wait);
+
+	return packetlen;
+}
+
+/**
+ * @note THERE IS NO MUTEX LOCK IN THIS FUNCTION!
+ * because we're only called from one location, pullbulk, where the lock
+ * is already held.
+ */
+usbmux_client_t find_client(usbmux_tcp_header * recv_header)
+{
+	// remember, as we're looking for the client, the receive header is
+	// coming from the USB into our client. This means that when we check
+	// the src/dst ports, we need to reverse them.
+	usbmux_client_t retval = NULL;
+
+	// just for debugging check, I'm going to convert the numbers to host-endian.
+	uint16_t hsport = ntohs(recv_header->sport);
+	uint16_t hdport = ntohs(recv_header->dport);
+
+	pthread_mutex_lock(&usbmuxmutex);
+	int i;
+	for (i = 0; i < clients; i++) {
+		uint16_t csport = ntohs(connlist[i]->header->sport);
+		uint16_t cdport = ntohs(connlist[i]->header->dport);
+
+		if (hsport == cdport && hdport == csport) {
+			retval = connlist[i];
+			break;
+		}
+	}
+	pthread_mutex_unlock(&usbmuxmutex);
+
+	return retval;
+}
+
+/** pull in a big USB bulk packet and distribute it to queues appropriately.
+ */
+int usbmux_pullbulk(usbmux_device_t device)
+{
+	if (!device)
+		return -EINVAL;
+
+	int res = 0;
+	static const int DEFAULT_CAPACITY = 128 * 1024;
+	if (device->usbReceive.buffer == NULL) {
+		device->usbReceive.capacity = DEFAULT_CAPACITY;
+		device->usbReceive.buffer = malloc(device->usbReceive.capacity);
+		device->usbReceive.leftover = 0;
+	}
+	// start the cursor off just ahead of the leftover.
+	char *cursor = &device->usbReceive.buffer[device->usbReceive.leftover];
+	// pull in content, note that the amount we can pull is capacity minus leftover
+	int readlen =
+		recv_from_device_timeout(device, cursor,
+								 device->usbReceive.capacity -
+								 device->usbReceive.leftover, 3000);
+	if (readlen < 0) {
+		res = readlen;
+		//fprintf(stderr, "recv_from_device_timeout gave us an error.\n");
+		readlen = 0;
+	}
+	if (readlen > 0) {
+		//fprintf(stdout, "recv_from_device_timeout pulled an extra %d bytes\n", readlen);
+	}
+	// the amount of content we have to work with is the remainder plus
+	// what we managed to read
+	device->usbReceive.leftover += readlen;
+
+	// reset the cursor to the front of that buffer and work through
+	// trying to decode packets out of them.
+	cursor = device->usbReceive.buffer;
+	while (1) {
+		// check if there's even sufficient data to decode a header
+		if (device->usbReceive.leftover < HEADERLEN)
+			break;
+		usbmux_tcp_header *header = (usbmux_tcp_header *) cursor;
+
+		log_debug_msg("%s: recv_from_device_timeout (%d --> %d)\n",
+					  __func__, ntohs(header->sport),
+					  ntohs(header->dport));
+
+		// now that we have a header, check if there is sufficient data
+		// to construct a full packet, including its data
+		uint32_t packetlen = ntohl(header->length);
+		if ((uint32_t) device->usbReceive.leftover < packetlen) {
+			fprintf(stderr,
+					"%s: not enough data to construct a full packet\n",
+					__func__);
+			break;
+		}
+		// ok... find the client this packet will get stuffed to.
+		usbmux_client_t client = find_client(header);
+		if (client == NULL) {
+			log_debug_msg
+				("WARNING: client for packet cannot be found. dropping packet.\n");
+		} else {
+			// stuff the data
+			log_debug_msg
+				("%s: found client, calling append_receive_buffer\n",
+				 __func__);
+			append_receive_buffer(client, cursor);
+
+			// perhaps this is too general, == -ECONNRESET
+			//  might be a better check here
+			if (client->error < 0) {
+				pthread_mutex_lock(&client->mutex);
+				if (client->cleanup) {
+					pthread_mutex_unlock(&client->mutex);
+					log_debug_msg("freeing up connection (%d->%d)\n",
+								  ntohs(client->header->sport),
+								  ntohs(client->header->dport));
+					delete_connection(client);
+				} else {
+					pthread_mutex_unlock(&client->mutex);
+				}
+			}
+		}
+
+		// move the cursor and account for the consumption
+		cursor += packetlen;
+		device->usbReceive.leftover -= packetlen;
+	}
+
+	// now, we need to manage any leftovers.
+	// I'm going to manage the leftovers by alloc'ing a new block and
+	// copyingthe leftovers to it. This is just to prevent problems with
+	// memory moves where there may be overlap. Besides, the leftovers
+	// should be small enough that this copy is minimal in overhead.
+	//
+	// if there are no leftovers, we just leave the datastructure as is,
+	// and re-use the block next time.
+	if (device->usbReceive.leftover > 0
+		&& cursor != device->usbReceive.buffer) {
+		log_debug_msg("%s: we got a leftover, so handle it\n", __func__);
+		char *newbuff = malloc(DEFAULT_CAPACITY);
+		memcpy(newbuff, cursor, device->usbReceive.leftover);
+		free(device->usbReceive.buffer);
+		device->usbReceive.buffer = newbuff;
+		device->usbReceive.capacity = DEFAULT_CAPACITY;
+	}
+
+	return res;
+}
+
+/**
+ * return the error code stored in usbmux_client_t structure,
+ * e.g. non-zero when an usb read error occurs.
+ *
+ * @param client the usbmux client
+ *
+ * @return 0 or a negative errno value.
+ */
+int usbmux_get_error(usbmux_client_t client)
+{
+	if (!client) {
+		return 0;
+	}
+	return client->error;
+}
+
+/** This function reads from the client's recv_buffer.
+ *
+ * @param client The client to receive data from.
+ * @param data Where to put the data we receive. 
+ * @param datalen How much data to read.
+ * @param timeout How many milliseconds to wait for data
+ *
+ * @return 0 on success or a negative errno value on failure.
+ */
+int usbmux_recv_timeout(usbmux_client_t client, char *data,
+						uint32_t datalen, uint32_t * recv_bytes,
+						int timeout)
+{
+
+	if (!client || !data || datalen == 0 || !recv_bytes)
+		return -EINVAL;
+
+	if (client->error < 0)
+		return client->error;
+
+	pthread_mutex_lock(&client->mutex);
+
+	if (timeout > 0 && (client->recv_buffer == NULL || client->r_len == 0)) {
+		struct timespec ts;
+		clock_gettime(CLOCK_REALTIME, &ts);
+		ts.tv_sec += timeout / 1000;
+		ts.tv_nsec += (timeout - ((int) (timeout / 1000)) * 1000) * 1000;
+		pthread_cond_timedwait(&client->wait, &client->mutex, &ts);
+	}
+
+	*recv_bytes = 0;
+	if (client->recv_buffer != NULL && client->r_len > 0) {
+		uint32_t foolen = datalen;
+		if ((int) foolen > client->r_len)
+			foolen = client->r_len;
+		memcpy(data, client->recv_buffer, foolen);
+		*recv_bytes = foolen;
+
+		// preserve any left-over unread amounts.
+		int remainder = client->r_len - foolen;
+		if (remainder > 0) {
+			char *newbuf = malloc(remainder);
+			memcpy(newbuf, client->recv_buffer + foolen, remainder);
+			client->r_len = remainder;
+			free(client->recv_buffer);
+			client->recv_buffer = newbuf;
+		} else {
+			free(client->recv_buffer);
+			client->recv_buffer = NULL;
+			client->r_len = 0;
+		}
+	}
+
+	pthread_mutex_unlock(&client->mutex);
+
+	return 0;
+}