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query.go
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query.go
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package postgres
import (
"encoding/csv"
"encoding/json"
"fmt"
"io"
"github.com/rs/zerolog/log"
)
func (s *PostgresServer) QueryNDJson(query string, writer io.Writer) error {
r, w := io.Pipe()
// errChan := make(chan error)
go func() {
queryErr := s.QueryJSON(query, w)
if queryErr != nil {
w.CloseWithError(queryErr)
} else {
w.Close()
}
}()
dec := json.NewDecoder(r)
// read open bracket
_, err := dec.Token()
if err != nil {
return err
}
// TODO: stream all of this instead of decoding
// while the array contains values
for dec.More() {
var m map[string]any
err := dec.Decode(&m)
if err != nil {
return err
// log.Fatal(err)
}
j, e := json.Marshal(m)
if e != nil {
return e
}
_, err = writer.Write(j)
if err != nil {
return err
}
_, err = writer.Write([]byte{'\n'})
if err != nil {
return err
}
}
// read closing bracket
_, err = dec.Token()
if err != nil {
return err
}
return nil
}
func (s *PostgresServer) QueryJSON(query string, writer io.Writer) error {
rows, err := s.conn.Query(query)
if err != nil {
log.Error().Err(err).Msg("failed to execute query")
return err
}
defer rows.Close()
columns, err := rows.Columns()
if err != nil {
log.Error().Err(err).Msg("failed to get column names")
return err
}
values := make([]interface{}, len(columns))
valuePtrs := make([]interface{}, len(columns))
for i := range columns {
valuePtrs[i] = &values[i]
}
_, err = writer.Write([]byte("["))
if err != nil {
log.Error().Err(err).Msg("failed to write JSON array start:")
return err
}
firstRow := true
encoder := json.NewEncoder(writer)
for rows.Next() {
err := rows.Scan(valuePtrs...)
if err != nil {
log.Error().Err(err).Msg("failed to scan row values")
return err
}
jsonObject := make(map[string]interface{})
for i, column := range columns {
jsonObject[column] = values[i]
}
if !firstRow {
_, err = writer.Write([]byte(","))
if err != nil {
log.Error().Err(err).Msg("failed to write JSON array separator")
return err
}
} else {
firstRow = false
}
err = encoder.Encode(jsonObject)
if err != nil {
log.Error().Err(err).Msg("failed to marshal JSON")
return err
}
}
_, err = writer.Write([]byte("]"))
if err != nil {
log.Error().Err(err).Msg("failed to write JSON array end")
return err
}
if err := rows.Err(); err != nil {
log.Error().Err(err).Msg("failed to iterate over all rows")
return err
}
return nil
}
func (s *PostgresServer) QueryCSV(query string, writer io.Writer) error {
rows, err := s.conn.Query(query)
if err != nil {
log.Error().Err(err).Msg("failed to execute query")
return err
}
defer rows.Close()
columns, err := rows.Columns()
if err != nil {
log.Error().Err(err).Msg("failed to get column names")
return err
}
values := make([]interface{}, len(columns))
valuePtrs := make([]interface{}, len(columns))
for i := range columns {
valuePtrs[i] = &values[i]
}
encoder := csv.NewWriter(writer)
// Write column names to the writer
err = encoder.Write(columns)
if err != nil {
log.Error().Err(err).Msg("failed to write column names")
return err
}
for rows.Next() {
err := rows.Scan(valuePtrs...)
if err != nil {
log.Error().Err(err).Msg("failed to scan row values")
return err
}
csvRow := make([]string, len(columns))
for i, value := range values {
if value == nil {
csvRow[i] = "null"
} else {
csvRow[i] = fmt.Sprintf("%v", value)
}
}
err = encoder.Write(csvRow)
if err != nil {
log.Error().Err(err).Msg("failed to write CSV row")
return err
}
}
if err := rows.Err(); err != nil {
log.Error().Err(err).Msg("failed to iterate rows")
return err
}
encoder.Flush()
return nil
}