cli: handle OOM by directly streaming output.

We use raw malloc here, again, to handle the failure cases more easily.

I tested it with this hack, then ran the result through `jq --stream '.'`
before and after to make sure it was the same.

    diff --git a/cli/lightning-cli.c b/cli/lightning-cli.c
    index f840c0786..d83555a51 100644
    --- a/cli/lightning-cli.c
    +++ b/cli/lightning-cli.c
    @@ -295,6 +295,14 @@ static void oom_dump(int fd, char *resp, size_t resp_len, size_t off)
     	exit(0);
     }
     
    +static void *xrealloc(void *p, size_t len)
    +{
    +	if (len > 1000000)
    +		return NULL;
    +	return realloc(p, len);
    +}
    +#define realloc xrealloc
    +
     int main(int argc, char *argv[])
     {
     	setup_locale();

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

cli/test/run-large-input.c

@@ -13,6 +13,8 @@ int test_connect(int sockfd, const struct sockaddr *addr,
 		 socklen_t addrlen);
 int test_getpid(void);
 int test_printf(const char *format, ...);
+void *test_malloc(size_t n);
+void *test_realloc(void *p, size_t n);
 
 #define main test_main
 #define read test_read
@@ -20,6 +22,8 @@ int test_printf(const char *format, ...);
 #define connect test_connect
 #define getpid test_getpid
 #define printf test_printf
+#define malloc test_malloc
+#define realloc test_realloc
 
   #include "../lightning-cli.c"
 #undef main
@@ -55,6 +59,17 @@ int test_printf(const char *fmt UNUSED, ...)
 static char *response;
 static size_t response_off, max_read_return;
 
+void *test_malloc(size_t n)
+{
+	return tal_arr(response, u8, n);
+}
+
+void *test_realloc(void *p, size_t n)
+{
+	tal_resize(&p, n);
+	return p;
+}
+
 ssize_t test_read(int fd UNUSED, void *buf, size_t len)
 {
 	if (len > max_read_return)