GUACAMOLE-662: Merge correct behavior of nested socket.

src/libguac/socket-nest.c

@@ -25,80 +25,237 @@
 
 #include <stddef.h>
 #include <stdlib.h>
+#include <string.h>
 #include <unistd.h>
 
-#define GUAC_SOCKET_NEST_BUFFER_SIZE 8192
+/**
+ * The maximum number of bytes to buffer before sending a "nest" instruction.
+ * As some of the 8 KB space available for each instruction will be taken up by
+ * the "nest" opcode and other parameters, and 1 KB will be more than enough
+ * space for that extra data, this space is reduced to an even 7 KB.
+ */
+#define GUAC_SOCKET_NEST_BUFFER_SIZE 7168
 
-typedef struct __guac_socket_nest_data {
+/**
+ * Internal data associated with an open socket which writes via a series of
+ * "nest" instructions to some underlying, parent socket.
+ */
+typedef struct guac_socket_nest_data {
 
+    /**
+     * The underlying socket which should be used to write "nest" instructions.
+     */
     guac_socket* parent;
-    char buffer[GUAC_SOCKET_NEST_BUFFER_SIZE];
+
+    /**
+     * The arbitrary index of the nested socket, assigned at time of
+     * allocation.
+     */
     int index;
 
-} __guac_socket_nest_data;
+    /**
+     * The number of bytes currently in the main write buffer.
+     */
+    int written;
 
-ssize_t __guac_socket_nest_write_handler(guac_socket* socket,
-        const void* buf, size_t count) {
+    /**
+     * The main write buffer. Bytes written go here before being flushed
+     * as nest instructions. Space is included for the null terminator
+     * required by guac_protocol_send_nest().
+     */
+    char buffer[GUAC_SOCKET_NEST_BUFFER_SIZE];
 
-    __guac_socket_nest_data* data = (__guac_socket_nest_data*) socket->data;
-    unsigned char* source = (unsigned char*) buf;
+    /**
+     * Lock which is acquired when an instruction is being written, and
+     * released when the instruction is finished being written.
+     */
+    pthread_mutex_t socket_lock;
 
-    /* Current location in destination buffer during copy */
-    char* current = data->buffer;
+    /**
+     * Lock which protects access to the internal buffer of this socket,
+     * guaranteeing atomicity of writes and flushes.
+     */
+    pthread_mutex_t buffer_lock;
 
-    /* Number of bytes remaining in source buffer */
-    int remaining = count;
+} guac_socket_nest_data;
 
-    /* If we can't actually store that many bytes, reduce number of bytes
-     * expected to be written */
-    if (remaining > GUAC_SOCKET_NEST_BUFFER_SIZE)
-        remaining = GUAC_SOCKET_NEST_BUFFER_SIZE;
+/**
+ * Flushes the contents of the output buffer of the given socket immediately,
+ * without first locking access to the output buffer. This function must ONLY
+ * be called if the buffer lock has already been acquired.
+ *
+ * @param socket
+ *     The guac_socket to flush.
+ *
+ * @return
+ *     Zero if the flush operation was successful, non-zero otherwise.
+ */
+static ssize_t guac_socket_nest_flush(guac_socket* socket) {
 
-    /* Current offset within destination buffer */
-    int offset;
+    guac_socket_nest_data* data = (guac_socket_nest_data*) socket->data;
 
-    /* Number of characters before start of next character */
-    int skip = 0;
+    /* Flush remaining bytes in buffer */
+    if (data->written > 0) {
 
-    /* Copy UTF-8 characters into buffer */
-    for (offset = 0; offset < GUAC_SOCKET_NEST_BUFFER_SIZE; offset++) {
+        /* Determine length of buffer containing complete UTF-8 characters
+         * (buffer may end with a partial, multi-byte character) */
+        int length = 0;
+        while (length < data->written)
+            length += guac_utf8_charsize(*(data->buffer + length));
 
-        /* Get next byte */
-        unsigned char c = *source;
-        remaining--;
+        /* Add null terminator, preserving overwritten character for later
+         * restoration (guac_protocol_send_nest() requires null-terminated
+         * strings) */
+        char overwritten = data->buffer[length];
+        data->buffer[length] = '\0';
 
-        /* If skipping, then skip */
-        if (skip > 0) skip--;
+        /* Write ALL bytes in buffer as nest instruction */
+        int retval = guac_protocol_send_nest(data->parent, data->index, data->buffer);
 
-        /* Otherwise, determine next skip value, and increment length */
-        else {
+        /* Restore original value overwritten by null terminator */
+        data->buffer[length] = overwritten;
 
-            /* Determine skip value (size in bytes of rest of character) */
-            skip = guac_utf8_charsize(c) - 1;
+        if (retval)
+            return 1;
 
-            /* If not enough bytes to complete character, break */
-            if (skip > remaining)
-                break;
-
-        }
-
-        /* Store byte */
-        *current = c;
-
-        /* Advance to next character */
-        source++;
-        current++;
+        /* Shift any remaining data to beginning of buffer */
+        memcpy(data->buffer, data->buffer + length, data->written - length);
+        data->written -= length;
 
     }
 
-    /* Append null-terminator */
-    *current = 0;
+    return 0;
 
-    /* Send nest instruction containing read UTF-8 segment */
-    guac_protocol_send_nest(data->parent, data->index, data->buffer);
+}
 
-    /* Return number of bytes actually written */
-    return offset;
+/**
+ * Flushes the internal buffer of the given guac_socket, writing all data
+ * to the underlying socket using "nest" instructions.
+ *
+ * @param socket
+ *     The guac_socket to flush.
+ *
+ * @return
+ *     Zero if the flush operation was successful, non-zero otherwise.
+ */
+static ssize_t guac_socket_nest_flush_handler(guac_socket* socket) {
+
+    int retval;
+    guac_socket_nest_data* data = (guac_socket_nest_data*) socket->data;
+
+    /* Acquire exclusive access to buffer */
+    pthread_mutex_lock(&(data->buffer_lock));
+
+    /* Flush contents of buffer */
+    retval = guac_socket_nest_flush(socket);
+
+    /* Relinquish exclusive access to buffer */
+    pthread_mutex_unlock(&(data->buffer_lock));
+
+    return retval;
+
+}
+
+/**
+ * Writes the contents of the buffer to the output buffer of the given socket,
+ * flushing the output buffer as necessary, without first locking access to the
+ * output buffer. This function must ONLY be called if the buffer lock has
+ * already been acquired.
+ *
+ * @param socket
+ *     The guac_socket to write the given buffer to.
+ *
+ * @param buf
+ *     The buffer to write to the given socket.
+ *
+ * @param count
+ *     The number of bytes in the given buffer.
+ *
+ * @return
+ *     The number of bytes written, or a negative value if an error occurs
+ *     during write.
+ */
+static ssize_t guac_socket_nest_write_buffered(guac_socket* socket,
+        const void* buf, size_t count) {
+
+    size_t original_count = count;
+    const char* current = buf;
+    guac_socket_nest_data* data = (guac_socket_nest_data*) socket->data;
+
+    /* Append to buffer, flush if necessary */
+    while (count > 0) {
+
+        int chunk_size;
+
+        /* Calculate space remaining, including one extra byte for the null
+         * terminator added upon flush */
+        int remaining = sizeof(data->buffer) - data->written - 1;
+
+        /* If no space left in buffer, flush and retry */
+        if (remaining == 0) {
+
+            /* Abort if error occurs during flush */
+            if (guac_socket_nest_flush(socket))
+                return -1;
+
+            /* Retry buffer append */
+            continue;
+
+        }
+
+        /* Calculate size of chunk to be written to buffer */
+        chunk_size = count;
+        if (chunk_size > remaining)
+            chunk_size = remaining;
+
+        /* Update output buffer */
+        memcpy(data->buffer + data->written, current, chunk_size);
+        data->written += chunk_size;
+
+        /* Update provided buffer */
+        current += chunk_size;
+        count   -= chunk_size;
+
+    }
+
+    /* All bytes have been written, possibly some to the internal buffer */
+    return original_count;
+
+}
+
+/**
+ * Appends the provided data to the internal buffer for future writing. The
+ * actual write attempt will occur only upon flush, or when the internal buffer
+ * is full.
+ *
+ * @param socket
+ *     The guac_socket being write to.
+ *
+ * @param buf
+ *     The arbitrary buffer containing the data to be written.
+ *
+ * @param count
+ *     The number of bytes contained within the buffer.
+ *
+ * @return
+ *     The number of bytes written, or -1 if an error occurs.
+ */
+static ssize_t guac_socket_nest_write_handler(guac_socket* socket,
+        const void* buf, size_t count) {
+
+    int retval;
+    guac_socket_nest_data* data = (guac_socket_nest_data*) socket->data;
+    
+    /* Acquire exclusive access to buffer */
+    pthread_mutex_lock(&(data->buffer_lock));
+
+    /* Write provided data to buffer */
+    retval = guac_socket_nest_write_buffered(socket, buf, count);
+
+    /* Relinquish exclusive access to buffer */
+    pthread_mutex_unlock(&(data->buffer_lock));
+
+    return retval;
 
 }
 
@@ -113,29 +270,63 @@ ssize_t __guac_socket_nest_write_handler(guac_socket* socket,
  *     Zero if the data was successfully freed, non-zero otherwise. This
  *     implementation always succeeds, and will always return zero.
  */
-static int __guac_socket_nest_free_handler(guac_socket* socket) {
+static int guac_socket_nest_free_handler(guac_socket* socket) {
 
     /* Free associated data */
-    __guac_socket_nest_data* data = (__guac_socket_nest_data*) socket->data;
+    guac_socket_nest_data* data = (guac_socket_nest_data*) socket->data;
     free(data);
 
     return 0;
 
 }
 
+/**
+ * Acquires exclusive access to the given socket.
+ *
+ * @param socket
+ *     The guac_socket to which exclusive access is required.
+ */
+static void guac_socket_nest_lock_handler(guac_socket* socket) {
+
+    guac_socket_nest_data* data = (guac_socket_nest_data*) socket->data;
+
+    /* Acquire exclusive access to socket */
+    pthread_mutex_lock(&(data->socket_lock));
+
+}
+
+/**
+ * Relinquishes exclusive access to the given socket.
+ *
+ * @param socket
+ *     The guac_socket to which exclusive access is no longer required.
+ */
+static void guac_socket_nest_unlock_handler(guac_socket* socket) {
+
+    guac_socket_nest_data* data = (guac_socket_nest_data*) socket->data;
+
+    /* Relinquish exclusive access to socket */
+    pthread_mutex_unlock(&(data->socket_lock));
+
+}
+
 guac_socket* guac_socket_nest(guac_socket* parent, int index) {
 
     /* Allocate socket and associated data */
     guac_socket* socket = guac_socket_alloc();
-    __guac_socket_nest_data* data = malloc(sizeof(__guac_socket_nest_data));
+    guac_socket_nest_data* data = malloc(sizeof(guac_socket_nest_data));
 
-    /* Store file descriptor as socket data */
+    /* Store nested socket details as socket data */
     data->parent = parent;
+    data->index = index;
     socket->data = data;
 
-    /* Set write and free handlers */
-    socket->write_handler  = __guac_socket_nest_write_handler;
-    socket->free_handler   = __guac_socket_nest_free_handler;
+    /* Set relevant handlers */
+    socket->write_handler  = guac_socket_nest_write_handler;
+    socket->lock_handler   = guac_socket_nest_lock_handler;
+    socket->unlock_handler = guac_socket_nest_unlock_handler;
+    socket->flush_handler  = guac_socket_nest_flush_handler;
+    socket->free_handler   = guac_socket_nest_free_handler;
 
     return socket;