Postgres Example (#490)

* creating postgres example - fixes #489

* postgres example glide fix

* all the changes

* use fn call

* removing func.yaml

* removing build.sh

* test.sh cleanup

examples/postgres/func.go

@@ -0,0 +1,103 @@
+package main
+
+import (
+	"bytes"
+	"database/sql"
+	"encoding/json"
+	"io/ioutil"
+	"log"
+	"os"
+	"strconv"
+
+	"github.com/pkg/errors"
+
+	_ "github.com/lib/pq"
+)
+
+var (
+	// command to execute, 'SELECT' or 'INSERT'
+	command = os.Getenv("HEADER_COMMAND")
+	// postgres host:port, e.g. 'postgres:5432'
+	server = os.Getenv("HEADER_SERVER")
+	// postgres table name
+	table = os.Getenv("HEADER_TABLE")
+)
+
+func main() {
+	req, err := ioutil.ReadAll(os.Stdin)
+	if err != nil {
+		log.Fatal(errors.Wrap(err, "failed to read stdin"))
+	}
+
+	db, err := sql.Open("postgres", "postgres://postgres@" + server + "?sslmode=disable")
+	if err != nil {
+		log.Println("Failed to connect to postgres server")
+		log.Fatal(err)
+		return
+	}
+
+	switch command {
+	case "SELECT":
+		if resp, err := selectCommand(req, db); err != nil {
+			log.Fatal(errors.Wrap(err, "select command failed"))
+		} else {
+			log.Println(resp)
+		}
+	case "INSERT":
+		if err := insertCommand(req, db); err != nil {
+			log.Fatal(errors.Wrap(err, "insert command failed"))
+		}
+	default:
+		log.Fatalf("invalid command: %q", command)
+	}
+}
+
+func selectCommand(req []byte, db *sql.DB) (string, error) {
+	// Parse request JSON
+	var params map[string]interface{}
+	if err := json.Unmarshal(req, &params); err != nil {
+		return "", errors.Wrap(err, "failed to parse json")
+	}
+
+	// Build query and gather arguments
+	var query bytes.Buffer
+	var args []interface{}
+
+	query.WriteString("SELECT json_agg(t) FROM (SELECT * FROM ")
+	query.WriteString(table)
+	query.WriteString(" WHERE")
+	first := true
+	arg := 1
+	for k, v := range params {
+		args = append(args, v)
+
+		if !first {
+			query.WriteString(" AND")
+		}
+		query.WriteString(" ")
+		query.WriteString(k)
+		query.WriteString("=$")
+		query.WriteString(strconv.Itoa(arg))
+		arg += 1
+		first = false
+	}
+	query.WriteString(") AS t")
+
+	// Execute query
+	r := db.QueryRow(query.String(), args...)
+	var resp string
+	if err := r.Scan(&resp); err != nil {
+		return "", errors.Wrap(err, "failed to execute select query")
+	}
+
+	return resp, nil
+}
+
+func insertCommand(req []byte, db *sql.DB) error {
+	q := "INSERT INTO " + table + " SELECT * FROM json_populate_record(null::" + table + ", $1)"
+	_, err := db.Exec(q, req)
+	if  err != nil {
+		return errors.Wrap(err, "Failed to execute insert query")
+	}
+	return nil
+}