{"record":{"id":"e3ec048d4eb611ad","repo":"gocolly/colly","slug":"errmissingurl","errorCode":"ErrMissingURL","errorMessage":"Missing URL","messagePattern":"Missing URL","errorType":"error_code","errorClass":null,"httpStatus":null,"severity":"error","filePath":"colly.go","lineNumber":225,"sourceCode":"// The key type is unexported to prevent collisions with context keys defined in\n// other packages.\ntype key int\n\n// ProxyURLKey is the context key for the request proxy address.\nconst (\n\tProxyURLKey key = iota\n\tCheckRevisitKey\n)\n\n// The prefix for environment variables of Colly settings\nconst envVariablePrefix = \"COLLY_\"\n\nvar (\n\t// ErrForbiddenDomain is the error thrown if visiting\n\t// a domain which is not allowed in AllowedDomains\n\tErrForbiddenDomain = errors.New(\"Forbidden domain\")\n\t// ErrMissingURL is the error type for missing URL errors\n\tErrMissingURL = errors.New(\"Missing URL\")\n\t// ErrMaxDepth is the error type for exceeding max depth\n\tErrMaxDepth = errors.New(\"Max depth limit reached\")\n\t// ErrForbiddenURL is the error thrown if visiting\n\t// a URL which is not allowed by URLFilters\n\tErrForbiddenURL = errors.New(\"ForbiddenURL\")\n\n\t// ErrNoURLFiltersMatch is the error thrown if visiting\n\t// a URL which is not allowed by URLFilters\n\tErrNoURLFiltersMatch = errors.New(\"No URLFilters match\")\n\t// ErrRobotsTxtBlocked is the error type for robots.txt errors\n\tErrRobotsTxtBlocked = errors.New(\"URL blocked by robots.txt\")\n\t// ErrNoCookieJar is the error type for missing cookie jar\n\tErrNoCookieJar = errors.New(\"Cookie jar is not available\")\n\t// ErrNoPattern is the error type for LimitRules without patterns\n\tErrNoPattern = errors.New(\"No pattern defined in LimitRule\")\n\t// ErrEmptyProxyURL is the error type for empty Proxy URL list\n\tErrEmptyProxyURL = errors.New(\"Proxy URL list is empty\")\n\t// ErrAbortedAfterHeaders is the error returned when OnResponseHeaders aborts the transfer.","sourceCodeStart":207,"sourceCodeEnd":243,"githubUrl":"https://github.com/gocolly/colly/blob/17d1d6ca92bd32a5651f34256bf7a2855c967f65/colly.go#L207-L243","documentation":"ErrMissingURL is returned when Visit() is called with an empty URL string. Colly cannot construct a request without a target URL, so it fails fast before any network I/O. It guards against programming mistakes such as an unset variable or a failed string extraction.","triggerScenarios":"Calling c.Visit(\"\") or c.Visit(u) where u is the empty string; passing the result of an extraction/attribute lookup that came back empty (e.g. href=\"\" or a missing query parameter); building the URL from optional config that was not provided.","commonSituations":"Scraping loops where a link attribute is missing on some pages so href is \"\"; command-line/config-driven crawlers where the --url flag or env var was never set; concatenating URL parts and ending up with an empty string.","solutions":["Check the argument before calling Visit: only call it when len(u) > 0","Log the URL value at the call site to find where the empty string originates","For collected links, verify the attribute exists (e.g. e.Attr(\"href\") != \"\") before queueing","If the URL comes from config/env, validate it at startup"],"exampleFix":"// before\nu := e.Attr(\"href\")\nc.Visit(u) // panics into ErrMissingURL when href=\"\"\n// after\nu := e.Attr(\"href\")\nif u != \"\" {\n    c.Visit(u)\n}","handlingStrategy":"validation","validationCode":"if target == \"\" {\n    return fmt.Errorf(\"no URL to visit\")\n}\nu, err := url.Parse(target)\nif err != nil || u.Scheme == \"\" || u.Host == \"\" {\n    return fmt.Errorf(\"invalid URL %q\", target)\n}","typeGuard":"func isNonEmptyURL(s string) bool {\n    u, err := url.Parse(s)\n    return err == nil && s != \"\" && u.Host != \"\"\n}","tryCatchPattern":"if err := c.Visit(target); err != nil {\n    if errors.Is(err, colly.ErrMissingURL) {\n        log.Printf(\"empty URL at %s, skipping\", callSite)\n        return nil\n    }\n    return err\n}","preventionTips":["Guard every Visit call with a non-empty check","Validate href/attribute lookups before queueing links","Validate config/env-provided URLs at startup"],"tags":["colly","scraping","empty-argument","go"],"backgroundTag":"missing-required-argument","analyzedSha":"17d1d6ca92bd32a5651f34256bf7a2855c967f65","analyzedAt":"2026-08-30T21:32:31.579Z","schemaVersion":2},"datasetVersion":"2026-08-30T23:17:21.991Z"}