Patchwork hg_open: the function that opens the connection with cmdserver

diff --git a/hglib/client.c b/hglib/client.c
new file mode 100644
--- /dev/null
+++ b/hglib/client.c
@@ -0,0 +1,171 @@ 
+#include <errno.h>
+#include <fcntl.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/types.h>
+
+#include "client.h"
+#include "utils.h"
+
+#define HGPATH "hg"
+
+/*
+ * The function will read the header from the command server and will 
+ * save it to handle pointer
+ * */
+hg_header *hg_read_header(hg_handle *handle)
+{
+	uint32_t length;
+	char ch_char;
+
+	if(!handle) {
+		errno = EINVAL;
+		return NULL;
+	}
+
+	if(handle->bytes_on_pipe == 0){
+		if(read(handle->p_read, &ch_char, 1) < 0){
+			return NULL;
+		}
+		if(read(handle->p_read, &length, sizeof(uint32_t)) < 0){
+			return NULL;
+		}
+		handle->header->length = swap_uint32(length);
+		handle->bytes_on_pipe = handle->header->length;
+		switch(ch_char){
+			case 'o':
+				handle->header->channel = o;
+				break;
+			case 'e':
+				handle->header->channel = e;
+				break;
+			case 'r':
+				handle->header->channel = r;
+				break;
+			case 'I':
+				handle->header->channel = I;
+				break;
+			case 'L':
+				handle->header->channel = L;
+				break;
+			default:
+				handle->header->channel = wrong_channel;
+				break;
+		}
+	}
+	return handle->header;
+}
+
+/**
+ * \brief Reading the hello msg from cmd server.
+ *
+ * After the connection, the command server sends a hello message.
+ * The message contains the command server capabilities and the messages
+ * encoding.
+ * \param handle The handle of the connection, wherewith I want to communicate
+ * \retval  0 if succesfull 
+ * \retval -1 to indicate an error, with errno set appropriately
+ * 
+ * errno can be:
+ *       - EINVAL  - Invalid argument (handle it's set to a null pointer)
+ *       - read(2) command errors
+ * */
+int read_hello(hg_handle *handle)
+{
+	char *buffer;
+	hg_header *ch;
+	int nc;
+
+	if(!handle) {
+		errno = EINVAL;
+		return -1;
+	}
+
+	ch = hg_read_header(handle);
+
+	if(ch->length == 0){
+		return -1;
+	}
+
+	buffer = malloc(ch->length + 1);
+
+	if(nc = read(handle->p_read, buffer, ch->length), nc < 0){
+		free(buffer);
+		return -1;
+	}
+	buffer[ch->length] = '\0';
+	handle->bytes_on_pipe -= nc;
+
+	free(buffer);
+
+	return 0;
+}
+
+/*
+ * Open the connection with the mercurial command server.
+ * */
+hg_handle *hg_open(const char *path, char *encoding)
+{
+	hg_handle *handle = malloc(sizeof(hg_handle));
+	handle->header = malloc(sizeof(hg_header));
+	/* len("%s serve --cmdserver pipe --config ui.interactive=True") = 52 */
+	char *command = malloc(strlen(HGPATH) + 53);
+	int wpipe[2];
+	int rpipe[2];
+	int c_write;
+	int c_read;
+	pid_t childpid;
+
+	sprintf(command,
+		"%s serve --cmdserver pipe --config ui.interactive=True",
+		HGPATH);
+
+	if (path){
+		command = realloc(command, strlen(command) + strlen(path) + 5);
+		sprintf(command, "%s -R %s", command, path);
+	}
+
+	if (pipe(wpipe) < 0 || pipe(rpipe) < 0) {
+		return NULL;
+	}
+	handle->p_read = rpipe[0];
+	c_write = rpipe[1];
+	c_read = wpipe[0];
+	handle->p_write = wpipe[1];
+	handle->protect = 0;
+	handle->bytes_on_pipe = 0;
+
+	if ((childpid = fork()) < 0) {
+		return NULL;
+
+	} else if (childpid == 0) {	/* child */
+		close(handle->p_write);
+		close(handle->p_read);
+		if(dup2(c_read, STDIN_FILENO) < 0){
+			return NULL;
+		}
+		close(c_read);
+		if(dup2(c_write, STDOUT_FILENO) < 0){
+			return NULL;
+		}
+		close(c_write);
+		if(execl("/bin/sh", "sh", "-c", command, NULL) < 0){
+			return NULL;
+		}
+	} else {	/* parent */
+		close(c_read);
+		close(c_write);
+	}
+
+	free(command);
+
+	if(read_hello(handle) < 0)
+		return NULL;
+
+	handle->out_data = NULL;
+	handle->out_data_size = 0;
+	return handle;
+}
+
diff --git a/hglib/client.h b/hglib/client.h
--- a/hglib/client.h
+++ b/hglib/client.h
@@ -1,4 +1,4 @@ 
-ifndef _CLIENT_H_
+#ifndef _CLIENT_H_
 #define _CLIENT_H_
 
 #include <errno.h>
diff --git a/hglib/utils.c b/hglib/utils.c
new file mode 100644
--- /dev/null
+++ b/hglib/utils.c
@@ -0,0 +1,17 @@ 
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdarg.h>
+
+#include "utils.h"
+
+/* 
+ * Byte swap unsigned int
+ * */
+uint32_t swap_uint32(uint32_t val)
+{
+	val = ((val << 8) & 0xFF00FF00) | ((val >> 8) & 0xFF00FF);
+	return (val << 16) | (val >> 16);
+}
+
diff --git a/hglib/utils.h b/hglib/utils.h
new file mode 100644
--- /dev/null
+++ b/hglib/utils.h
@@ -0,0 +1,13 @@ 
+#ifndef _UTILS_CHG_H_
+#define _UTILS_CHG_H_
+
+#include <stdint.h>
+
+/** 
+ * \brief Byte swap unsigned int
+ * \param val an uint32_t integer
+ * \retval uint32_t the bigendian form of val value
+ * */
+uint32_t swap_uint32(uint32_t val);
+
+#endif