237069c827
- add jz_bm_materials.revision (default 1), read-only for GORM
- bump it only on content changes (models.ReviseMaterial)
- PUT /materials/{id} locks the row and answers 409 to a stale revision
- management answers carry revision and updated_at, the student detail
carries revision
59 lines
2.1 KiB
Go
59 lines
2.1 KiB
Go
package api
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import (
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"context"
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"net/http"
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"git.golem15.com/golem15/summercms/modules/wire"
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"git.golem15.com/jakub/sm-bm-plugin/models"
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"gorm.io/gorm"
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)
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// A write of a material's content may carry the revision the writer last
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// read (D-01, D-04). When it does and the stored revision differs, the write
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// is refused with 409 and nothing is written; when it does not, the write
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// overwrites as before, so callers that never send a revision keep working.
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// The compare and the write run on the row locked FOR UPDATE, so two writers
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// holding the same revision cannot both succeed.
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// conflictMessage is the message of a 409 answer to a stale revision.
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const conflictMessage = "The material was changed since the revision you sent."
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// staleRevision reports whether a write that sent revision sent must be
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// refused: true when it sent one and it is not the stored one.
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func staleRevision(sent *uint, stored uint) bool {
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return sent != nil && *sent != stored
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}
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// revise bumps the revision of material id inside tx when its content
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// differs from before (models.ReviseMaterial). Every content writer of the
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// API calls it after its write.
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func (h *Handlers) revise(ctx context.Context, tx *gorm.DB, id uint, before string) error {
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_, _, err := models.ReviseMaterial(tx.WithContext(ctx), id, before)
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return err
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}
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// writeConflict answers 409 to a write that sent a stale revision, with the
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// current revision, its updated_at and the material as the management API
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// shows it, so the writer can diff or pull. Under MCP the body is left out,
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// as in every other MCP answer.
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func writeConflict(w http.ResponseWriter, r *http.Request, db *gorm.DB, id uint) {
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var cur models.Material
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if err := preloadMaterial(db).First(&cur, id).Error; err != nil {
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writeOpaque500(w)
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return
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}
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people, err := loadMaterialPeople(db, cur)
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if err != nil {
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writeOpaque500(w)
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return
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}
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wire.WriteJSON(w, http.StatusConflict, map[string]any{
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"error": true,
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"message": conflictMessage,
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"revision": cur.Revision,
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"updated_at": models.FormatDateTime(cur.UpdatedAt),
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"data": managedMaterialView(newManagedMaterialJSON(cur, people), viaMCP(r), false),
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})
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}
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