feat: add direct links download functionality

- Implemented a new task type for handling direct links downloads.
- Added command handler for downloading multiple links via /dl command.
- Introduced progress tracking for direct link downloads.
- Enhanced filename parsing to support various encoding scenarios.
- Updated enums to include direct links as a task type.
- Refactored existing task structures to accommodate new functionality.
- Improved error handling and logging throughout the download process.

core/tasks/directlinks/util.go

@@ -0,0 +1,205 @@
+package directlinks
+
+import (
+	"mime"
+	"net/url"
+	"strings"
+	"unicode/utf8"
+
+	"golang.org/x/text/encoding/simplifiedchinese"
+)
+
+// parseFilename extracts filename from Content-Disposition header
+// It handles multiple encoding scenarios:
+// 1. RFC 5987/RFC 2231 format: filename*=UTF-8”%E6%B5%8B%E8%AF%95.zip (preferred, checked first)
+// 2. MIME encoded-word: filename="=?UTF-8?B?5rWL6K+VLnppcA==?="
+// 3. URL-encoded: filename="%E6%B5%8B%E8%AF%95.zip"
+// 4. Plain ASCII filename
+//
+// The key fix is checking filename*= first before mime.ParseMediaType, because
+// some servers send Content-Disposition headers with invalid characters that cause
+// mime.ParseMediaType to fail, but the filename*= parameter is still valid.
+func parseFilename(contentDisposition string) string {
+	// First, try to find filename*= (RFC 5987 format, most reliable for non-ASCII)
+	if filename := parseFilenameExtended(contentDisposition); filename != "" {
+		return filename
+	}
+
+	// Try standard MIME parsing for regular filename= parameter
+	_, params, err := mime.ParseMediaType(contentDisposition)
+	if err == nil {
+		if filename := params["filename"]; filename != "" {
+			return decodeFilenameParam(filename)
+		}
+	}
+
+	// Fallback: manual parsing if mime.ParseMediaType fails
+	return parseFilenameFallback(contentDisposition)
+}
+
+// parseFilenameExtended parses RFC 5987/RFC 2231 extended parameter format
+// Format: filename*=charset'language'value (e.g., UTF-8”%E6%B5%8B%E8%AF%95.zip)
+func parseFilenameExtended(cd string) string {
+	// Look for filename*= (case-insensitive)
+	lower := strings.ToLower(cd)
+	idx := strings.Index(lower, "filename*=")
+	if idx == -1 {
+		return ""
+	}
+
+	// Extract the value after filename*=
+	value := cd[idx+len("filename*="):]
+
+	// Find the end of the value (next ; or end of string)
+	if endIdx := strings.Index(value, ";"); endIdx != -1 {
+		value = value[:endIdx]
+	}
+	value = strings.TrimSpace(value)
+
+	// Parse charset'language'encoded-value format
+	// Common format: UTF-8''%E6%B5%8B%E8%AF%95.zip
+	parts := strings.SplitN(value, "''", 2)
+	if len(parts) == 2 {
+		// parts[0] is charset (e.g., "UTF-8")
+		// parts[1] is percent-encoded value
+		decoded, err := url.QueryUnescape(parts[1])
+		if err == nil {
+			return decoded
+		}
+	}
+
+	// Try with single quote delimiter as well (some servers use this)
+	parts = strings.SplitN(value, "'", 3)
+	if len(parts) >= 3 {
+		decoded, err := url.QueryUnescape(parts[2])
+		if err == nil {
+			return decoded
+		}
+	}
+
+	return ""
+}
+
+// TryUrlQueryUnescape tries to unescape a URL-encoded string.
+//
+// If unescaping fails, it returns the original string.
+func tryUrlQueryUnescape(s string) string {
+	if decoded, err := url.QueryUnescape(s); err == nil {
+		return decoded
+	}
+	return s
+}
+
+// decodeFilenameParam decodes a filename parameter value
+// Handles MIME encoded-word, URL encoding, and GBK encoding fallback
+func decodeFilenameParam(filename string) string {
+	// Check if the filename is MIME encoded-word (e.g., =?UTF-8?B?...?=)
+	if strings.HasPrefix(filename, "=?") {
+		decoder := new(mime.WordDecoder)
+		// Some servers use "UTF8" instead of "UTF-8", create a normalized copy
+		normalizedFilename := strings.Replace(filename, "UTF8", "UTF-8", 1)
+		if decoded, err := decoder.Decode(normalizedFilename); err == nil {
+			return decoded
+		}
+	}
+
+	// Try URL decoding
+	decoded := tryUrlQueryUnescape(filename)
+
+	// Check if the result is valid UTF-8. If not, try GBK decoding.
+	// This handles the case where Chinese Windows servers send GBK-encoded filenames
+	// which appear as garbled characters (e.g., "下载地址.zip" -> "���ص�ַ.zip")
+	if !utf8.ValidString(decoded) {
+		if gbkDecoded := tryDecodeGBK(decoded); gbkDecoded != "" {
+			return gbkDecoded
+		}
+	}
+
+	return decoded
+}
+
+// gbkDecoder is a reusable GBK decoder for better performance
+var gbkDecoder = simplifiedchinese.GBK.NewDecoder()
+
+// tryDecodeGBK attempts to decode a string as GBK/GB2312/GB18030 encoding
+// Returns empty string if decoding fails or result is not valid UTF-8
+func tryDecodeGBK(s string) string {
+	// GBK uses 1-2 bytes per character. Single-byte chars are 0x00-0x7F (ASCII compatible).
+	// Double-byte chars have first byte 0x81-0xFE and second byte 0x40-0xFE.
+	// Skip if string is empty or all ASCII (valid UTF-8)
+	if len(s) == 0 {
+		return ""
+	}
+
+	// Create a fresh decoder since the transform state may be corrupted
+	decoder := gbkDecoder
+	decoded, err := decoder.Bytes([]byte(s))
+	if err != nil {
+		return ""
+	}
+	result := string(decoded)
+	if utf8.ValidString(result) {
+		return result
+	}
+	return ""
+}
+
+// parseFilenameFallback manually parses filename= when mime.ParseMediaType fails
+func parseFilenameFallback(cd string) string {
+	// Look for filename= (case-insensitive)
+	lower := strings.ToLower(cd)
+	idx := strings.Index(lower, "filename=")
+	if idx == -1 {
+		return ""
+	}
+
+	// Skip "filename=" prefix
+	value := cd[idx+len("filename="):]
+
+	// Find the end of the value
+	if endIdx := strings.Index(value, ";"); endIdx != -1 {
+		value = value[:endIdx]
+	}
+	value = strings.TrimSpace(value)
+
+	// Remove quotes if present
+	if len(value) >= 2 {
+		if (value[0] == '"' && value[len(value)-1] == '"') ||
+			(value[0] == '\'' && value[len(value)-1] == '\'') {
+			value = value[1 : len(value)-1]
+		}
+	}
+
+	return decodeFilenameParam(value)
+}
+
+var progressUpdatesLevels = []struct {
+	size        int64 // 文件大小阈值
+	stepPercent int   // 每多少 % 更新一次
+}{
+	{10 << 20, 100},
+	{50 << 20, 50},
+	{200 << 20, 20},
+	{500 << 20, 10},
+}
+
+func shouldUpdateProgress(total, downloaded int64, lastUpdatePercent int) bool {
+	if total <= 0 || downloaded <= 0 {
+		return false
+	}
+
+	percent := int((downloaded * 100) / total)
+	if percent <= lastUpdatePercent {
+		return false
+	}
+
+	step := progressUpdatesLevels[len(progressUpdatesLevels)-1].stepPercent
+	for _, lvl := range progressUpdatesLevels {
+		if total < lvl.size {
+			step = lvl.stepPercent
+			break
+		}
+	}
+
+	return percent >= lastUpdatePercent+step
+}