Move ipc_send_message and ipc_recv_message to libi3

Make i3-msg and src/ipc.c use it

libi3/ipc_recv_message.c

@@ -0,0 +1,81 @@
+/*
+ * vim:ts=4:sw=4:expandtab
+ *
+ * i3 - an improved dynamic tiling window manager
+ *
+ * © 2009-2011 Michael Stapelberg and contributors
+ *
+ * See file LICENSE for license information.
+ *
+ */
+#include <string.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <unistd.h>
+
+#include <i3/ipc.h>
+
+#include "libi3.h"
+
+/*
+ * Reads a message from the given socket file descriptor and stores its length
+ * (reply_length) as well as a pointer to its contents (reply).
+ *
+ * Returns -1 when read() fails, errno will remain.
+ * Returns -2 when the IPC protocol is violated (invalid magic, unexpected
+ * message type, EOF instead of a message). Additionally, the error will be
+ * printed to stderr.
+ * Returns 0 on success.
+ *
+ */
+int ipc_recv_message(int sockfd, uint32_t message_type,
+                     uint32_t *reply_length, uint8_t **reply) {
+    /* Read the message header first */
+    uint32_t to_read = strlen(I3_IPC_MAGIC) + sizeof(uint32_t) + sizeof(uint32_t);
+    char msg[to_read];
+    char *walk = msg;
+
+    uint32_t read_bytes = 0;
+    while (read_bytes < to_read) {
+        int n = read(sockfd, msg + read_bytes, to_read);
+        if (n == -1)
+            return -1;
+        if (n == 0) {
+            fprintf(stderr, "IPC: received EOF instead of reply\n");
+            return -2;
+        }
+
+        read_bytes += n;
+        to_read -= n;
+    }
+
+    if (memcmp(walk, I3_IPC_MAGIC, strlen(I3_IPC_MAGIC)) != 0) {
+        fprintf(stderr, "IPC: invalid magic in reply\n");
+        return -2;
+    }
+
+    walk += strlen(I3_IPC_MAGIC);
+    *reply_length = *((uint32_t*)walk);
+    walk += sizeof(uint32_t);
+    if (*((uint32_t*)walk) != message_type) {
+        fprintf(stderr, "IPC: unexpected reply type (got %d, expected %d)\n", *((uint32_t*)walk), message_type);
+        return -2;
+    }
+    walk += sizeof(uint32_t);
+
+    *reply = smalloc(*reply_length);
+
+    to_read = *reply_length;
+    read_bytes = 0;
+    while (read_bytes < to_read) {
+        int n = read(sockfd, *reply + read_bytes, to_read);
+        if (n == -1)
+            return -1;
+
+        read_bytes += n;
+        to_read -= n;
+    }
+
+    return 0;
+}