Refactor swap.c to use getline() instead of buf-filling

This drops a lot of code and even though we are using a common function,
the specification of only the needed things keeps it very efficient and
even more efficient in memory and time than the previous solution.

components/swap.c

@@ -1,52 +1,71 @@
 /* See LICENSE file for copyright and license details. */
 #include <errno.h>
+#include <stdint.h>
 #include <stdio.h>
+#include <stdlib.h>
 #include <string.h>
 
 #include "../util.h"
 
 #if defined(__linux__)
-	static size_t
-	pread(const char *path, char *buf, size_t bufsiz)
+	static int
+	get_swap_info(long *s_total, long *s_free, long *s_cached)
 	{
 		FILE *fp;
-		size_t bytes_read;
-
-		if (!(fp = fopen(path, "r"))) {
-			warn("fopen '%s':", path);
-			return 0;
-		}
-		if (!(bytes_read = fread(buf, sizeof(char), bufsiz, fp))) {
-			warn("fread '%s':", path);
-			fclose(fp);
-			return 0;
+		struct {
+			const char *name;
+			const size_t len;
+			long *var;
+		} ent[] = {
+			{ "SwapTotal",  sizeof("SwapTotal") - 1,  s_total  },
+			{ "SwapFree",   sizeof("SwapFree") - 1,   s_free   },
+			{ "SwapCached", sizeof("SwapCached") - 1, s_cached },
+		};
+		size_t line_len = 0, i, left;
+		char *line = NULL;
+
+		/* get number of fields we want to extract */
+		for (i = 0, left = 0; i < LEN(ent); i++) {
+			if (ent[i].var) {
+				left++;
+			}
+		}
+
+		if (!(fp = fopen("/proc/meminfo", "r"))) {
+			warn("fopen '/proc/meminfo':");
+			return 1;
 		}
-		fclose(fp);
 
-		buf[bytes_read] = '\0';
+		/* read file line by line and extract field information */
+		while (left > 0 && getline(&line, &line_len, fp) >= 0) {
+			for (i = 0; i < LEN(ent); i++) {
+				if (ent[i].var &&
+				    !strncmp(line, ent[i].name, ent[i].len)) {
+					sscanf(line + ent[i].len + 1, "%ld kB\n",
+					       ent[i].var);
+					left--;
+					break;
+				}
+			}
+		}
+		free(line);
+		if (ferror(fp)) {
+			warn("getline '/proc/meminfo':");
+			return 1;
+		}
 
-		return bytes_read;
+		fclose(fp);
+		return 0;
 	}
 
 	const char *
 	swap_free(void)
 	{
-		long total, free;
-		char *match;
-
-		if (!pread("/proc/meminfo", buf, sizeof(buf) - 1)) {
-			return NULL;
-		}
-
-		if (!(match = strstr(buf, "SwapTotal"))) {
-			return NULL;
-		}
-		sscanf(match, "SwapTotal: %ld kB\n", &total);
+		long free;
 
-		if (!(match = strstr(buf, "SwapFree"))) {
+		if (get_swap_info(NULL, &free, NULL)) {
 			return NULL;
 		}
-		sscanf(match, "SwapFree: %ld kB\n", &free);
 
 		return fmt_human(free * 1024, 1024);
 	}
@@ -55,28 +74,8 @@
 	swap_perc(void)
 	{
 		long total, free, cached;
-		char *match;
-
-		if (!pread("/proc/meminfo", buf, sizeof(buf) - 1)) {
-			return NULL;
-		}
-
-		if (!(match = strstr(buf, "SwapTotal"))) {
-			return NULL;
-		}
-		sscanf(match, "SwapTotal: %ld kB\n", &total);
-
-		if (!(match = strstr(buf, "SwapCached"))) {
-			return NULL;
-		}
-		sscanf(match, "SwapCached: %ld kB\n", &cached);
-
-		if (!(match = strstr(buf, "SwapFree"))) {
-			return NULL;
-		}
-		sscanf(match, "SwapFree: %ld kB\n", &free);
 
-		if (total == 0) {
+		if (get_swap_info(&total, &free, &cached) || total == 0) {
 			return NULL;
 		}
 
@@ -87,16 +86,10 @@
 	swap_total(void)
 	{
 		long total;
-		char *match;
-
-		if (!pread("/proc/meminfo", buf, sizeof(buf) - 1)) {
-			return NULL;
-		}
 
-		if (!(match = strstr(buf, "SwapTotal"))) {
+		if (get_swap_info(&total, NULL, NULL)) {
 			return NULL;
 		}
-		sscanf(match, "SwapTotal: %ld kB\n", &total);
 
 		return fmt_human(total * 1024, 1024);
 	}
@@ -105,26 +98,10 @@
 	swap_used(void)
 	{
 		long total, free, cached;
-		char *match;
-
-		if (!pread("/proc/meminfo", buf, sizeof(buf) - 1)) {
-			return NULL;
-		}
-
-		if (!(match = strstr(buf, "SwapTotal"))) {
-			return NULL;
-		}
-		sscanf(match, "SwapTotal: %ld kB\n", &total);
-
-		if (!(match = strstr(buf, "SwapCached"))) {
-			return NULL;
-		}
-		sscanf(match, "SwapCached: %ld kB\n", &cached);
 
-		if (!(match = strstr(buf, "SwapFree"))) {
+		if (get_swap_info(&total, &free, &cached)) {
 			return NULL;
 		}
-		sscanf(match, "SwapFree: %ld kB\n", &free);
 
 		return fmt_human((total - free - cached) * 1024, 1024);
 	}