examples: network: fix Win32 linking errors due to getline

The getline(3) function call is not part of ISO C and, most importantly,
it is not implemented on Microsoft Windows platforms. As our networking
example code makes use of getline, this breaks builds on MSVC and MinGW.
As this code wasn't built prior to the previous commit, this was never
noticed.

Fix the error by instead implementing a `readline` function, which
simply reads the password from stdin until it reads a newline
character.

(cherry picked from commit bf15dbf6)

examples/network/common.c

@@ -16,6 +16,43 @@
 # define UNUSED(x) x
 #endif
 
+static int readline(char **out)
+{
+	int c, error = 0, length = 0, allocated = 0;
+	char *line = NULL;
+
+	errno = 0;
+
+	while ((c = getchar()) != EOF) {
+		if (length == allocated) {
+			allocated += 16;
+
+			if ((line = realloc(line, allocated)) == NULL) {
+				error = -1;
+				goto error;
+			}
+		}
+
+		if (c == '\n')
+			break;
+
+		line[length++] = c;
+	}
+
+	if (errno != 0) {
+		error = -1;
+		goto error;
+	}
+
+	line[length] = '\0';
+	*out = line;
+	line = NULL;
+	error = length;
+error:
+	free(line);
+	return error;
+}
+
 int cred_acquire_cb(git_cred **out,
 		const char * UNUSED(url),
 		const char * UNUSED(username_from_url),
@@ -26,14 +63,14 @@ int cred_acquire_cb(git_cred **out,
 	int error;
 
 	printf("Username: ");
-	if (getline(&username, NULL, stdin) < 0) {
+	if (readline(&username) < 0) {
 		fprintf(stderr, "Unable to read username: %s", strerror(errno));
 		return -1;
 	}
 
 	/* Yup. Right there on your terminal. Careful where you copy/paste output. */
 	printf("Password: ");
-	if (getline(&password, NULL, stdin) < 0) {
+	if (readline(&password) < 0) {
 		fprintf(stderr, "Unable to read password: %s", strerror(errno));
 		free(username);
 		return -1;