add fmt_iso8601

fmt.h

@@ -137,6 +137,9 @@ size_t fmt_humank(char* dest,unsigned long long l);
 /* "Sun, 06 Nov 1994 08:49:37 GMT" */
 size_t fmt_httpdate(char* dest,time_t t);
 
+/* "2014-05-27T19:22:16.247Z" */
+size_t fmt_iso8601(char* dest,time_t t);
+
 #define FMT_UTF8 5
 #define FMT_ASN1LENGTH 17 /* enough space to hold 2^128-1 */
 #define FMT_ASN1TAG 19 /* enough space to hold 2^128-1 */

fmt/fmt_iso8601.c

@@ -0,0 +1,31 @@
+#include "fmt.h"
+#include "byte.h"
+#include <time.h>
+
+static unsigned int fmt_2digits(char* dest,int i) {
+  dest[0]=(char)((i/10)+'0');
+  dest[1]=(char)((i%10)+'0');
+  return 2;
+}
+
+size_t fmt_iso8601(char* dest,time_t t) {
+  struct tm* x=gmtime(&t);
+  size_t i;
+
+  if (dest==0) return sizeof("2014-05-27T19:22:16Z")-1;
+  /* "2014-05-27T19:22:16Z" */
+  i=fmt_2digits(dest,(x->tm_year+1900)/100);
+  i+=fmt_2digits(dest+i,(x->tm_year+1900)%100);
+  dest[i++]='-';
+  i+=fmt_2digits(dest+i,x->tm_mon+1);
+  dest[i++]='-';
+  i+=fmt_2digits(dest+i,x->tm_mday);
+  dest[i++]='T';
+  i+=fmt_2digits(dest+i,x->tm_hour);
+  i+=fmt_str(dest+i,":");
+  i+=fmt_2digits(dest+i,x->tm_min);
+  i+=fmt_str(dest+i,":");
+  i+=fmt_2digits(dest+i,x->tm_sec);
+  i+=fmt_str(dest+i,"Z");
+  return i;
+}

test/fmt_iso8691.c

@@ -0,0 +1,10 @@
+#include <fmt.h>
+#include <assert.h>
+#include <unistd.h>
+
+int main() {
+  char buf[1024];
+  write(1,buf,fmt_iso8601(buf,0));
+  write(1,"\n",1);
+  return 0;
+}