René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"JSON errors: line numbers","articleBody":"Playground code:\r\n\r\n```go\r\npackage main\r\n\r\nimport (\r\n\t\"encoding/json\"\r\n\t\"fmt\"\r\n\t\"io\"\r\n\t\"strings\"\r\n)\r\n\r\n// (ab)using the fact that the JSON decoder has accumulated over all it's read plus it's working on the new buffer\r\n// it's about to receive now.\r\ntype lineCounter struct {\r\n\tcommittedLines int\r\n\tcommittedBytes int64\r\n\r\n\tuncommitted      []byte\r\n\tuncommittedLines int\r\n}\r\n\r\nfunc (l *lineCounter) LineNumberFromOffset(offset int64) int {\r\n\tif offset \u003c l.committedBytes {\r\n\t\tpanic(\"offset \u003c l.committedBytes\")\r\n\t}\r\n\r\n\tintoUncommitted := offset - l.committedBytes\r\n\r\n\tlinesIntoUncommitted := countNewlines(l.uncommitted[:intoUncommitted])\r\n\r\n\treturn l.committedLines + linesIntoUncommitted\r\n}\r\n\r\nvar _ io.Writer = (*lineCounter)(nil)\r\n\r\nfunc (l *lineCounter) Write(buf []byte) (int, error) {\r\n\t// the fact that `Write()` was called means that the previous uncommitted buffer was consumed fully. \"commit\" now.\r\n\tl.committedBytes += int64(len(l.uncommitted))\r\n\tl.committedLines += l.uncommittedLines\r\n\r\n\tl.uncommittedLines = countNewlines(buf)\r\n\tl.uncommitted = buf\r\n\r\n\treturn len(buf), nil\r\n}\r\n\r\nfunc main() {\r\n\tlc := \u0026lineCounter{}\r\n\r\n\tjd := json.NewDecoder(io.TeeReader(strings.NewReader(`{\r\n\r\n\r\n\t\"Foo\": \"bar\"}`), lc))\r\n\terr := jd.Decode(\u0026struct{ Foo struct{} }{})\r\n\tif err != nil {\r\n\t\tfmt.Printf(\"err=%v pos=%d\\n\", err, lc.LineNumberFromOffset(jd.InputOffset()))\r\n\t}\r\n\r\n\tfmt.Println(\"Hello, 世界\")\r\n}\r\n\r\nfunc countNewlines(buf []byte) int {\r\n\tnewlines := 0\r\n\r\n\tfor _, ch := range buf {\r\n\t\tif ch == '\\n' {\r\n\t\t\tnewlines++\r\n\t\t}\r\n\t}\r\n\r\n\treturn newlines\r\n}\r\n\r\n```","author":{"url":"https://github.com/joonas-fi","@type":"Person","name":"joonas-fi"},"datePublished":"2023-09-11T12:21:24.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":1},"url":"https://github.com/24/gokit/issues/24"}