postgresql - 无法获取 Go http 返回错误； 'No data recieved'

Question

我正在尝试使用 Go 构建一个基本 API，它使用 PostgreSQL library 返回 SQL 查询的结果。 .

目前我可以让程序返回值，但我无法让它向用户返回失败的消息，即一些带有错误消息的 JSON。

我有一个错误函数如下:

func handleError(w http.ResponseWriter, err error) {
    if err != nil {
        log.Print(err.Error() + "\r\n") // Logging
        http.Error(w, err.Error(), http.StatusInternalServerError)
        return
    }
}

但是 http.Error 方法似乎没有返回任何东西。抛出的错误是数据库中不存在的表(记录到文本文件中:即 2016/01/11 23:28:19 pq:关系“building_roof”不存在

我的程序查询代码如下所示:

table := pq.QuoteIdentifier(table)
identifier := pq.QuoteIdentifier("ID")
rows, err := db.Query( fmt.Sprintf("SELECT %s, ST_AsText(geom) FROM %s WHERE %s = $1", identifier, table, identifier), feature)
handleError(w, err)

导致错误只会导致 Chrome 错误:

没有收到数据

ERR_EMPTY_RESPONSE

编辑完整代码:

package main

import (
    "fmt"
    "encoding/json"
    "os"
    "log"
    "net/http"
    "database/sql"
    "strings"
    "time"
    "github.com/lib/pq"
)


func handler(w http.ResponseWriter, r *http.Request) {

    f, err := os.OpenFile("pgdump_errorlog.txt", os.O_RDWR | os.O_CREATE | os.O_APPEND, 0666)
    log.Print("Couldn't open file")
    defer f.Close()
    log.SetOutput(f)

    // Timing
    start := time.Now()

    // Postgres Credentials
    const (
        DB_USER     = "postgres"
        DB_PASSWORD = "OMITTED" // Removed details !
        DB_PORT     = "OMITTED"
        DB_NAME     = "OMITTED"
    )

    // Postgres Connect
    dbinfo := fmt.Sprintf("user=%s password=%s dbname=%s port=%s sslmode=disable",
                           DB_USER, DB_PASSWORD, DB_NAME, DB_PORT)
    db, err := sql.Open("postgres", dbinfo)
    handleError(w, err)
    defer db.Close()

    table := r.FormValue("table")
    feature := r.FormValue("id")
    if table != "" {

        //Postgres Query
        var (
            id int
            geom string
        )

        table := pq.QuoteIdentifier(table)
        identifier := pq.QuoteIdentifier("ID")
        rows, qerr := db.Query( fmt.Sprintf("SELECT %s, ST_AsText(geom) FROM %s WHERE %s = $1", identifier, table, identifier), feature)
        handleError(w, err)
        defer rows.Close()
        for rows.Next() {
            err := rows.Scan(&id, &geom)
            handleError(w, err)
        }
        err = rows.Err()
        handleError(w, err)

        // Maniplate Strings
        returngeom := strings.Replace(geom, "1.#QNAN", "", -1)
        i := strings.Index(returngeom, "(")
        wkt := strings.TrimSpace(returngeom[:i])
        returngeom = returngeom[i:]

        type WTKJSON struct {
            WTKType   string
            Geometry  string
            Elapsed   time.Duration
        }

        returnjson := WTKJSON{Geometry:  returngeom, WTKType: wkt , Elapsed: time.Since(start)/1000000.0}
        json.NewEncoder(w).Encode(returnjson)

    }

}

func handleError(w http.ResponseWriter, err error) {
    if err != nil {
        log.Print(err.Error() + "\r\n") // Logging
        http.Error(w, err.Error(), http.StatusInternalServerError)
        return
    }
}


func main() {
    http.HandleFunc("/", handler)
    http.ListenAndServe(":8080", nil)
}

Answer 1

以下似乎允许我返回 JSON 错误:

func handleError(w http.ResponseWriter, err string) {
    type APIError struct {
        Error string
    }
    re, _ := json.Marshal(APIError{Error: err})
    io.WriteString(w, string(re))
}

这样使用:

rows, err := db.Query( fmt.Sprintf("SELECT %s, ST_AsText(geom) FROM %s WHERE %s = $1", identifier, table, identifier), feature)
        if err != nil {
            handleError(w, err.Error())
            return
        }

并不是说这是最好的方法，但对我来说很有效。