improve more error messages

src/main.zig

@@ -1,6 +1,7 @@
 const std = @import("std");
 const info = std.log.info;
 const debug = std.log.debug;
+const stderr = std.io.getStdErr().writer();
 const print = std.debug.print;
 const eql = std.mem.eql;
 const Allocator = std.mem.Allocator;
@@ -21,7 +22,9 @@ pub fn main() !void {
             },
             ArgumentError.UnknownParameter, //
             ArgumentError.MissingAuthenticatorParam, //
-            ArgumentError.MissingConfigLocation,
+            ArgumentError.MissingConfigLocation, //
+            ArgumentError.FailedToOpenConfigFile, //
+            ArgumentError.TooManyParsinErrors, //
             => {
                 // do nothing, error message is already written (because the message contains the name of the unknown parameter)
             },
@@ -167,7 +170,7 @@ fn zeroPad(allocator: Allocator, digits: u4, x: anytype) ![]u8 {
     return result;
 }
 
-const ArgumentError = error{ InvalidOtpAuthUrl, UnknownParameter, MissingConfigLocation, AuthenticatorNotFound, MissingAuthenticatorParam };
+const ArgumentError = error{ InvalidOtpAuthUrl, UnknownParameter, MissingConfigLocation, AuthenticatorNotFound, MissingAuthenticatorParam, FailedToOpenConfigFile, TooManyParsinErrors };
 
 fn parseArgs(allocator: Allocator, args: []const []const u8) !Args {
     var result = Args{
@@ -274,34 +277,65 @@ fn configLocation(allocator: Allocator) ![]const u8 {
 /// Reads the config file into a list of OtpAuthUrl.
 /// The caller should use an arena allocator and free the memory eventually.
 fn read_config(allocator: Allocator, config_location: []const u8) !ArrayList(OtpAuthUrl) {
-    const file = try std.fs.cwd().openFile(config_location, .{});
-    defer file.close();
+    const file_result = std.fs.cwd().openFile(config_location, .{});
+    if (file_result) |file| {
+        defer file.close();
 
-    var buf_reader = std.io.bufferedReader(file.reader());
-    var in_stream = buf_reader.reader();
+        var buf_reader = std.io.bufferedReader(file.reader());
+        var in_stream = buf_reader.reader();
 
-    var authenticators = std.ArrayList(OtpAuthUrl).init(allocator);
+        var authenticators = std.ArrayList(OtpAuthUrl).init(allocator);
 
-    var line_no: usize = 1;
-    while (try in_stream.readUntilDelimiterOrEofAlloc(allocator, '\n', 1024 * 1024)) |line| {
-        if (line.len > 0 and std.mem.trim(u8, line, " \r").len > 0) {
-            const authenticatorResult = parseOtpAuthUrl(allocator, line);
-            if (authenticatorResult) |authenticator| {
-                try authenticators.append(authenticator);
-            } else |err| {
-                switch (err) {
-                    error.InvalidOtpAuthUrl => {
-                        try std.io.getStdErr().writer().print("invalid otpauth url in line {d} in {s}\n", .{ line_no, config_location });
-                    },
-                    else => {
-                        return err;
-                    },
+        var number_of_errors: u32 = 0;
+        var line_no: usize = 1;
+        while (try in_stream.readUntilDelimiterOrEofAlloc(allocator, '\n', 1024 * 1024)) |line| {
+            if (line.len > 0 and std.mem.trim(u8, line, " \r").len > 0) {
+                const authenticatorResult = parseOtpAuthUrl(allocator, line);
+                if (authenticatorResult) |authenticator| {
+                    try authenticators.append(authenticator);
+                } else |err| {
+                    number_of_errors += 1;
+                    switch (err) {
+                        error.UnexpectedCharacter, error.InvalidFormat => {
+                            try stderr.print("Unexpected character in line {d} in file {s}. Line will be ignored.\n", .{ line_no, config_location });
+                            if (number_of_errors >= 10) {
+                                try stderr.print("too many parsing errors\n", .{});
+                                return ArgumentError.TooManyParsinErrors;
+                            }
+                        },
+                        error.InvalidOtpAuthUrl => {
+                            try std.io.getStdErr().writer().print("invalid otpauth url in line {d} in {s}\n", .{ line_no, config_location });
+                        },
+                        else => {
+                            return err;
+                        },
+                    }
                 }
             }
+            line_no += 1;
         }
-        line_no += 1;
+        return authenticators;
+    } else |err| {
+        //debug("file open error: {}\n", .{err});
+        switch (err) {
+            error.AccessDenied, //
+            error.BadPathName,
+            error.InvalidWtf8,
+            => {
+                try stderr.print("cannot open config file: {}\n", .{err});
+            },
+            error.FileNotFound => {
+                try stderr.print("config file not found. Create a new config file in $HOME/.zig-totp or $XDG_CONFIG_HOME/zig-totp.\n", .{});
+            },
+            error.IsDir => {
+                try stderr.print("the configuration location must be a file, but is a directory.\n", .{});
+            },
+            else => {
+                return err;
+            },
+        }
+        return ArgumentError.FailedToOpenConfigFile;
     }
-    return authenticators;
 }
 
 fn executeGetList(allocator: Allocator, config_location: []const u8) !std.ArrayList([]const u8) {