Add user configuration file support

Resolves #16.

Signed-off-by: Artem Senichev <artemsen@gmail.com>

README.md

@@ -54,6 +54,17 @@ Examples:
 - `PgUp` or `p`: Open previous file;
 - `Esc`, `Enter`, `F10` or `q`: Exit the program.
 
+## Configuration
+
+The viewer searches for the configuration file with name `config` in the
+following directories:
+- `$XDG_CONFIG_HOME/swayimg`
+- `$HOME/.config/swayimg`
+
+Sample file is available [here](https://github.com/artemsen/swayimg/blob/master/extra/swayimgrc).
+
+See `man swayimgrc` for details.
+
 ## Build and install
 
 ```

extra/swayimg.1

@@ -75,6 +75,9 @@ Exit the program.
 .SH ENVIRONMENT
 .IP \fISWAYSOCK\fR
 Path to the socket file used for Sway IPC.
+.\" related man pages
+.SH SEE ALSO
+swayimgrc(5)
 .\" link to homepage
 .SH BUGS
 For suggestions, comments, bug reports etc. visit the

extra/swayimgrc

@@ -0,0 +1,21 @@
+# Swayimg configuration file.
+
+# This file contains the default configuration.
+# The viewer searches for the config file in the following locations:
+# 1. $XDG_CONFIG_HOME/swayimg/config
+# 2. $HOME/.config/swayimg/config
+# See `man swayimgrc` for details.
+
+# Initial scale (default, fit, or real)
+scale = default
+
+# Start in full screen mode (yes/no)
+fullscreen = no
+
+# Background mode/color (grid or RGB, e.g. 112233)
+background = grid
+
+# Show image info: format, size, EXIF, and current scale (yes/no)
+info = no
+
+# vim: filetype=dosini

extra/swayimgrc.5

@@ -0,0 +1,50 @@
+.\" Swayimg configuration file format.
+.\" Copyright (C) 2022 Artem Senichev <artemsen@gmail.com>
+.TH SWAYIMG 5 2022-02-09 swayimg "Swayimg configuration"
+.SH NAME
+swayimgrc \- Swayimg configuration file
+.\" possible file locations
+.SH SYNOPSIS
+.SY \fI$XDG_CONFIG_HOME\fR/swayimg/config
+.SY \fI$HOME\fR/.config/swayimg/config
+.\" format description
+.SH DESCRIPTION
+.SS General format description
+The Swayimg configuration file is a text-based INI file used to override the
+default settings.
+.PP
+The basic element contained in the INI file is the key or property.
+Every key has a name and a value, delimited by an equals sign (=).
+The name appears to the left of the equals sign. The value can contain any
+character. Kay and values are case sensitive.
+.PP
+The number sign (#) at the beginning of the line indicates a comment.
+Empty lines and comments are ignored.
+.SS Properties
+.PP
+.IP "\fBscale\fR: initial image scale:"
+.nf
+\fIdefault\fR: 100% or less to fit to window;
+\fIfit\fR: fit to window;
+\fIreal\fR: real size (100%);
+.IP "\fBfullscreen\fR: start in dull screen mode, possible values are \fIyes\fR or \fIno\fR"
+.IP "\fBbackground\fR: background mode or color, possible values are \fIgrid\fR or RGB hex color (e.g. \fI1a2b3c\fR)"
+.IP "\fBinfo\fR: show image meta information: format, size, EXIF, and current scale, possible values are \fIyes\fR or \fIno\fR"
+.\" example file
+.SH EXAMPLES
+.EX
+# comment
+scale = default
+fullscreen = no
+background = grid
+info = no
+.EE
+.\" related man pages
+.SH SEE ALSO
+swayimg(1)
+.\" link to homepage
+.SH BUGS
+For suggestions, comments, bug reports etc. visit the
+.UR https://github.com/artemsen/swayimg
+project homepage
+.UE .

meson.build

@@ -82,6 +82,7 @@ xdg_shell_h = custom_target(
 # man installation
 if get_option('man')
   install_man('extra/swayimg.1')
+  install_man('extra/swayimgrc.5')
 endif
 
 # desktop file + icon

src/canvas.h

@@ -7,7 +7,7 @@
 #include <stdbool.h>
 #include <stdint.h>
 
-// Special bacground color: grid
+// Grid background mode id
 #define BACKGROUND_GRID UINT32_MAX
 
 // Convert color components from RGB to float

src/config.c

@@ -5,17 +5,137 @@
 
 #include <ctype.h>
 #include <errno.h>
+#include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <sys/types.h>
 
 config_t config = {
     .scale = scale_fit_or100,
     .background = BACKGROUND_GRID,
 };
 
+/**
+ * Apply property to configuration.
+ * @param[in] key property key
+ * @param[in] value property value
+ */
+static void apply_conf(const char* key, const char* value)
+{
+    const char* yes = "yes";
+    const char* no = "no";
+
+    if (strcmp(key, "scale") == 0) {
+        if (strcmp(value, "default") == 0) {
+            config.scale = scale_fit_or100;
+        } else if (strcmp(value, "fit") == 0) {
+            config.scale = scale_fit_window;
+        } else if (strcmp(value, "real") == 0) {
+            config.scale = scale_100;
+        }
+    } else if (strcmp(key, "fullscreen") == 0) {
+        if (strcmp(value, yes) == 0) {
+            config.fullscreen = true;
+        } else if (strcmp(value, no) == 0) {
+            config.fullscreen = false;
+        }
+    } else if (strcmp(key, "background") == 0) {
+        set_background(value);
+    } else if (strcmp(key, "info") == 0) {
+        if (strcmp(value, yes) == 0) {
+            config.show_info = true;
+        } else if (strcmp(value, no) == 0) {
+            config.show_info = false;
+        }
+    }
+}
+
+/**
+ * Open user's configuration file.
+ * @return file descriptior or NULL on errors
+ */
+static FILE* open_file(void)
+{
+    char path[64];
+    size_t len;
+    const char* postfix = "/swayimg/config";
+    const size_t postfix_len = strlen(postfix);
+
+    const char* config_dir = getenv("XDG_CONFIG_HOME");
+    if (config_dir) {
+        len = strlen(config_dir);
+        if (len < sizeof(path)) {
+            memcpy(path, config_dir, len + 1 /*last null*/);
+        } else {
+            len = 0;
+        }
+    } else {
+        config_dir = getenv("HOME");
+        len = config_dir ? strlen(config_dir) : 0;
+        if (len && len < sizeof(path)) {
+            memcpy(path, config_dir, len + 1 /*last null*/);
+            const char* dir = "/.config";
+            const size_t dlen = strlen(dir);
+            if (len + dlen < sizeof(path)) {
+                memcpy(path + len, dir, dlen + 1 /*last null*/);
+                len += dlen;
+            } else {
+                len = 0;
+            }
+        }
+    }
+
+    if (len && len + postfix_len < sizeof(path)) {
+        memcpy(path + len, postfix, postfix_len + 1 /*last null*/);
+        return fopen(path, "r");
+    }
+    return NULL;
+}
+
 void load_config(void)
 {
-    // todo
+    char* buff = NULL;
+    size_t buff_sz = 0;
+    ssize_t nread;
+
+    FILE* fd = open_file();
+    if (!fd) {
+        return;
+    }
+
+    while ((nread = getline(&buff, &buff_sz, fd)) != -1) {
+        const char* value;
+        char* delim;
+        char* line = buff;
+        // trim spaces
+        while (nread-- && isspace(line[nread])) {
+            line[nread] = 0;
+        }
+        while (*line && isspace(*line)) {
+            ++line;
+        }
+        if (!*line || *line == '#') {
+            continue; // skip empty lines and comments
+        }
+        delim = strchr(line, '=');
+        if (!delim) {
+            continue; // invalid format: delimiter not found
+        }
+        // trim spaces from start of value
+        value = delim + 1;
+        while (*value && isspace(*value)) {
+            ++value;
+        }
+        // trim spaces from key
+        *delim = 0;
+        while (line != delim && isspace(*--delim)) {
+            *delim = 0;
+        }
+        apply_conf(line, value);
+    }
+
+    free(buff);
+    fclose(fd);
 }
 
 bool set_scale(const char* value)

src/config.h

@@ -9,7 +9,7 @@
 typedef struct {
     scale_t scale;       ///< Initial scale
     rect_t window;       ///< Window geometry
-    uint32_t background; ///< Background color
+    uint32_t background; ///< Background mode/color
     bool fullscreen;     ///< Full screen mode
     bool show_info;      ///< Show image info
 } config_t;

src/main.c

@@ -81,7 +81,7 @@ int main(int argc, char* argv[])
             case 'b':
                 if (!set_background(optarg)) {
                     fprintf(stderr, "Invalid background: %s\n", optarg);
-                    fprintf(stderr, "Expected \"grid\" or RGB hex value.\n");
+                    fprintf(stderr, "Expected 'grid' or RGB hex value.\n");
                     return EXIT_FAILURE;
                 }
                 break;